Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Raslan, KarimAllah]

On Thu, 2018-07-05 at 14:51 +0100, Mark Rutland wrote:
> On Sun, Apr 15, 2018 at 12:26:44AM +0200, KarimAllah Ahmed wrote:
> > 
> > Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> > use the size of "requests" instead of the hard-coded '32'.
> > 
> > That gives us a bit more room again for arch-specific requests as we
> > already ran out of space for x86 due to the hard-coded check.
> > 
> > Cc: Paolo Bonzini 
> > Cc: Radim Krčmář 
> > Cc: k...@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: KarimAllah Ahmed 
> > ---
> >  include/linux/kvm_host.h | 10 +-
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 6930c63..fe4f46b 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
> >  #define KVM_REQUEST_ARCH_BASE 8
> >  
> >  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> > -   BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> > +   BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> > *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \
> > (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
> >  })
> >  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> > @@ -223,7 +223,7 @@ struct kvm_vcpu {
> > int vcpu_id;
> > int srcu_idx;
> > int mode;
> > -   unsigned long requests;
> > +   u64 requests;
> 
> The usual thing to do for bitmaps is something like:
> 
> #define KVM_REQUEST_NR(KVM_REQUEST_ARCH_BASE + 
> KVM_REQUEST_ARCH_NR)
> 
>   unsigned long requests[BITS_TO_LONGS(NR_KVM_REQUESTS)];
> 
> > 
> > unsigned long guest_debug;
> >  
> > int pre_pcpu;
> > @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> > kvm_vcpu *vcpu)
> >  * caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
> >  */
> > smp_wmb();
> > -   set_bit(req & KVM_REQUEST_MASK, >requests);
> > +   set_bit(req & KVM_REQUEST_MASK, (void *)>requests);
> 
> ... which wouldn't require a void cast to make the bit API functions
> happy (as these expect a pointer to the first unsigned long in the
> bitmap).

Ah, right! Good point.

Paolo,

Would you prefer to switch "requests" to a bitmap and 
update kvm_request_pending to handle this?

> 
> Thanks,
> Mark.
> 
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Raslan, KarimAllah]

On Thu, 2018-07-05 at 14:51 +0100, Mark Rutland wrote:
> On Sun, Apr 15, 2018 at 12:26:44AM +0200, KarimAllah Ahmed wrote:
> > 
> > Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> > use the size of "requests" instead of the hard-coded '32'.
> > 
> > That gives us a bit more room again for arch-specific requests as we
> > already ran out of space for x86 due to the hard-coded check.
> > 
> > Cc: Paolo Bonzini 
> > Cc: Radim Krčmář 
> > Cc: k...@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: KarimAllah Ahmed 
> > ---
> >  include/linux/kvm_host.h | 10 +-
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 6930c63..fe4f46b 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
> >  #define KVM_REQUEST_ARCH_BASE 8
> >  
> >  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> > -   BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> > +   BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> > *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \
> > (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
> >  })
> >  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> > @@ -223,7 +223,7 @@ struct kvm_vcpu {
> > int vcpu_id;
> > int srcu_idx;
> > int mode;
> > -   unsigned long requests;
> > +   u64 requests;
> 
> The usual thing to do for bitmaps is something like:
> 
> #define KVM_REQUEST_NR(KVM_REQUEST_ARCH_BASE + 
> KVM_REQUEST_ARCH_NR)
> 
>   unsigned long requests[BITS_TO_LONGS(NR_KVM_REQUESTS)];
> 
> > 
> > unsigned long guest_debug;
> >  
> > int pre_pcpu;
> > @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> > kvm_vcpu *vcpu)
> >  * caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
> >  */
> > smp_wmb();
> > -   set_bit(req & KVM_REQUEST_MASK, >requests);
> > +   set_bit(req & KVM_REQUEST_MASK, (void *)>requests);
> 
> ... which wouldn't require a void cast to make the bit API functions
> happy (as these expect a pointer to the first unsigned long in the
> bitmap).

Ah, right! Good point.

Paolo,

Would you prefer to switch "requests" to a bitmap and 
update kvm_request_pending to handle this?

> 
> Thanks,
> Mark.
> 
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Mark Rutland]

On Sun, Apr 15, 2018 at 12:26:44AM +0200, KarimAllah Ahmed wrote:
> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> use the size of "requests" instead of the hard-coded '32'.
> 
> That gives us a bit more room again for arch-specific requests as we
> already ran out of space for x86 due to the hard-coded check.
> 
> Cc: Paolo Bonzini 
> Cc: Radim Krčmář 
> Cc: k...@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed 
> ---
>  include/linux/kvm_host.h | 10 +-
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6930c63..fe4f46b 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQUEST_ARCH_BASE 8
>  
>  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> - BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> + BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \
>   (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
>  })
>  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> @@ -223,7 +223,7 @@ struct kvm_vcpu {
>   int vcpu_id;
>   int srcu_idx;
>   int mode;
> - unsigned long requests;
> + u64 requests;

The usual thing to do for bitmaps is something like:

#define KVM_REQUEST_NR  (KVM_REQUEST_ARCH_BASE + KVM_REQUEST_ARCH_NR)

unsigned long requests[BITS_TO_LONGS(NR_KVM_REQUESTS)];

>   unsigned long guest_debug;
>  
>   int pre_pcpu;
> @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> kvm_vcpu *vcpu)
>* caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
>*/
>   smp_wmb();
> - set_bit(req & KVM_REQUEST_MASK, >requests);
> + set_bit(req & KVM_REQUEST_MASK, (void *)>requests);

... which wouldn't require a void cast to make the bit API functions
happy (as these expect a pointer to the first unsigned long in the
bitmap).

Thanks,
Mark.

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Mark Rutland]

On Sun, Apr 15, 2018 at 12:26:44AM +0200, KarimAllah Ahmed wrote:
> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> use the size of "requests" instead of the hard-coded '32'.
> 
> That gives us a bit more room again for arch-specific requests as we
> already ran out of space for x86 due to the hard-coded check.
> 
> Cc: Paolo Bonzini 
> Cc: Radim Krčmář 
> Cc: k...@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed 
> ---
>  include/linux/kvm_host.h | 10 +-
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6930c63..fe4f46b 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQUEST_ARCH_BASE 8
>  
>  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> - BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> + BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \
>   (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
>  })
>  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> @@ -223,7 +223,7 @@ struct kvm_vcpu {
>   int vcpu_id;
>   int srcu_idx;
>   int mode;
> - unsigned long requests;
> + u64 requests;

The usual thing to do for bitmaps is something like:

#define KVM_REQUEST_NR  (KVM_REQUEST_ARCH_BASE + KVM_REQUEST_ARCH_NR)

unsigned long requests[BITS_TO_LONGS(NR_KVM_REQUESTS)];

>   unsigned long guest_debug;
>  
>   int pre_pcpu;
> @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> kvm_vcpu *vcpu)
>* caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
>*/
>   smp_wmb();
> - set_bit(req & KVM_REQUEST_MASK, >requests);
> + set_bit(req & KVM_REQUEST_MASK, (void *)>requests);

... which wouldn't require a void cast to make the bit API functions
happy (as these expect a pointer to the first unsigned long in the
bitmap).

Thanks,
Mark.

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Paolo Bonzini]

On 05/07/2018 14:22, Raslan, KarimAllah wrote:
>> They don't support atomics on double-word data.
> But they support atomics on single words. Of which there are two.
> We don't need atomic updates of the whole 64-bit quantity (a là 
> cmpxchg). Do we strictly need this to be atomic accross the 64-bit?
> 
> Looking at the use cases for "requests":
> 
> kvm_clear_request
> kvm_test_request
> kvm_request_pending
> kvm_check_request
> 
> ... and all of them would still work if the atomicity is only at the 
> word level, right?
> 

Good point!  Then yes, requests can be made 64 bit wide.

Paolo

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Paolo Bonzini]

On 05/07/2018 14:22, Raslan, KarimAllah wrote:
>> They don't support atomics on double-word data.
> But they support atomics on single words. Of which there are two.
> We don't need atomic updates of the whole 64-bit quantity (a là 
> cmpxchg). Do we strictly need this to be atomic accross the 64-bit?
> 
> Looking at the use cases for "requests":
> 
> kvm_clear_request
> kvm_test_request
> kvm_request_pending
> kvm_check_request
> 
> ... and all of them would still work if the atomicity is only at the 
> word level, right?
> 

Good point!  Then yes, requests can be made 64 bit wide.

Paolo

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Raslan, KarimAllah]

On Tue, 2018-05-22 at 17:47 +0200, Paolo Bonzini wrote:
> On 22/05/2018 17:42, Raslan, KarimAllah wrote:
> > 
> > On Mon, 2018-04-16 at 18:28 +0200, Paolo Bonzini wrote:
> > > 
> > > On 15/04/2018 00:26, KarimAllah Ahmed wrote:
> > > > 
> > > > 
> > > > Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check 
> > > > to
> > > > use the size of "requests" instead of the hard-coded '32'.
> > > > 
> > > > That gives us a bit more room again for arch-specific requests as we
> > > > already ran out of space for x86 due to the hard-coded check.
> > > > 
> > > > Cc: Paolo Bonzini 
> > > > Cc: Radim Krčmář 
> > > > Cc: k...@vger.kernel.org
> > > > Cc: linux-kernel@vger.kernel.org
> > > > Signed-off-by: KarimAllah Ahmed 
> > > 
> > > I'm afraid architectures like ARM 32 need this to be conditional (using
> > > Kconfig).
> > 
> > Why would using a 64-bit 'requests' be a problem for ARM32? Are you 
> > concerned about performance here or is there some symantic problem?
> 
> They don't support atomics on double-word data.

But they support atomics on single words. Of which there are two.
We don't need atomic updates of the whole 64-bit quantity (a là 
cmpxchg). Do we strictly need this to be atomic accross the 64-bit?

Looking at the use cases for "requests":

kvm_clear_request
kvm_test_request
kvm_request_pending
kvm_check_request

... and all of them would still work if the atomicity is only at the 
word level, right?

> 
> Paolo
> 
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Raslan, KarimAllah]

On Tue, 2018-05-22 at 17:47 +0200, Paolo Bonzini wrote:
> On 22/05/2018 17:42, Raslan, KarimAllah wrote:
> > 
> > On Mon, 2018-04-16 at 18:28 +0200, Paolo Bonzini wrote:
> > > 
> > > On 15/04/2018 00:26, KarimAllah Ahmed wrote:
> > > > 
> > > > 
> > > > Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check 
> > > > to
> > > > use the size of "requests" instead of the hard-coded '32'.
> > > > 
> > > > That gives us a bit more room again for arch-specific requests as we
> > > > already ran out of space for x86 due to the hard-coded check.
> > > > 
> > > > Cc: Paolo Bonzini 
> > > > Cc: Radim Krčmář 
> > > > Cc: k...@vger.kernel.org
> > > > Cc: linux-kernel@vger.kernel.org
> > > > Signed-off-by: KarimAllah Ahmed 
> > > 
> > > I'm afraid architectures like ARM 32 need this to be conditional (using
> > > Kconfig).
> > 
> > Why would using a 64-bit 'requests' be a problem for ARM32? Are you 
> > concerned about performance here or is there some symantic problem?
> 
> They don't support atomics on double-word data.

But they support atomics on single words. Of which there are two.
We don't need atomic updates of the whole 64-bit quantity (a là 
cmpxchg). Do we strictly need this to be atomic accross the 64-bit?

Looking at the use cases for "requests":

kvm_clear_request
kvm_test_request
kvm_request_pending
kvm_check_request

... and all of them would still work if the atomicity is only at the 
word level, right?

> 
> Paolo
> 
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Paolo Bonzini]

On 22/05/2018 17:42, Raslan, KarimAllah wrote:
> On Mon, 2018-04-16 at 18:28 +0200, Paolo Bonzini wrote:
>> On 15/04/2018 00:26, KarimAllah Ahmed wrote:
>>>
>>> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
>>> use the size of "requests" instead of the hard-coded '32'.
>>>
>>> That gives us a bit more room again for arch-specific requests as we
>>> already ran out of space for x86 due to the hard-coded check.
>>>
>>> Cc: Paolo Bonzini 
>>> Cc: Radim Krčmář 
>>> Cc: k...@vger.kernel.org
>>> Cc: linux-kernel@vger.kernel.org
>>> Signed-off-by: KarimAllah Ahmed 
>>
>> I'm afraid architectures like ARM 32 need this to be conditional (using
>> Kconfig).
> 
> Why would using a 64-bit 'requests' be a problem for ARM32? Are you 
> concerned about performance here or is there some symantic problem?

They don't support atomics on double-word data.

Paolo

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Paolo Bonzini]

On 22/05/2018 17:42, Raslan, KarimAllah wrote:
> On Mon, 2018-04-16 at 18:28 +0200, Paolo Bonzini wrote:
>> On 15/04/2018 00:26, KarimAllah Ahmed wrote:
>>>
>>> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
>>> use the size of "requests" instead of the hard-coded '32'.
>>>
>>> That gives us a bit more room again for arch-specific requests as we
>>> already ran out of space for x86 due to the hard-coded check.
>>>
>>> Cc: Paolo Bonzini 
>>> Cc: Radim Krčmář 
>>> Cc: k...@vger.kernel.org
>>> Cc: linux-kernel@vger.kernel.org
>>> Signed-off-by: KarimAllah Ahmed 
>>
>> I'm afraid architectures like ARM 32 need this to be conditional (using
>> Kconfig).
> 
> Why would using a 64-bit 'requests' be a problem for ARM32? Are you 
> concerned about performance here or is there some symantic problem?

They don't support atomics on double-word data.

Paolo

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Raslan, KarimAllah]

On Mon, 2018-04-16 at 18:28 +0200, Paolo Bonzini wrote:
> On 15/04/2018 00:26, KarimAllah Ahmed wrote:
> > 
> > Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> > use the size of "requests" instead of the hard-coded '32'.
> > 
> > That gives us a bit more room again for arch-specific requests as we
> > already ran out of space for x86 due to the hard-coded check.
> > 
> > Cc: Paolo Bonzini 
> > Cc: Radim Krčmář 
> > Cc: k...@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: KarimAllah Ahmed 
> 
> I'm afraid architectures like ARM 32 need this to be conditional (using
> Kconfig).

Why would using a 64-bit 'requests' be a problem for ARM32? Are you 
concerned about performance here or is there some symantic problem?

> 
> Thanks,
> 
> Paolo
> 
> > 
> > ---
> >  include/linux/kvm_host.h | 10 +-
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 6930c63..fe4f46b 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
> >  #define KVM_REQUEST_ARCH_BASE 8
> >  
> >  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> > -   BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> > +   BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> > *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \
> > (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
> >  })
> >  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> > @@ -223,7 +223,7 @@ struct kvm_vcpu {
> > int vcpu_id;
> > int srcu_idx;
> > int mode;
> > -   unsigned long requests;
> > +   u64 requests;
> > unsigned long guest_debug;
> >  
> > int pre_pcpu;
> > @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> > kvm_vcpu *vcpu)
> >  * caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
> >  */
> > smp_wmb();
> > -   set_bit(req & KVM_REQUEST_MASK, >requests);
> > +   set_bit(req & KVM_REQUEST_MASK, (void *)>requests);
> >  }
> >  
> >  static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
> > @@ -1132,12 +1132,12 @@ static inline bool kvm_request_pending(struct 
> > kvm_vcpu *vcpu)
> >  
> >  static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
> >  {
> > -   return test_bit(req & KVM_REQUEST_MASK, >requests);
> > +   return test_bit(req & KVM_REQUEST_MASK, (void *)>requests);
> >  }
> >  
> >  static inline void kvm_clear_request(int req, struct kvm_vcpu *vcpu)
> >  {
> > -   clear_bit(req & KVM_REQUEST_MASK, >requests);
> > +   clear_bit(req & KVM_REQUEST_MASK, (void *)>requests);
> >  }
> >  
> >  static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
> > 
> 
> 
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Raslan, KarimAllah]

On Mon, 2018-04-16 at 18:28 +0200, Paolo Bonzini wrote:
> On 15/04/2018 00:26, KarimAllah Ahmed wrote:
> > 
> > Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> > use the size of "requests" instead of the hard-coded '32'.
> > 
> > That gives us a bit more room again for arch-specific requests as we
> > already ran out of space for x86 due to the hard-coded check.
> > 
> > Cc: Paolo Bonzini 
> > Cc: Radim Krčmář 
> > Cc: k...@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: KarimAllah Ahmed 
> 
> I'm afraid architectures like ARM 32 need this to be conditional (using
> Kconfig).

Why would using a 64-bit 'requests' be a problem for ARM32? Are you 
concerned about performance here or is there some symantic problem?

> 
> Thanks,
> 
> Paolo
> 
> > 
> > ---
> >  include/linux/kvm_host.h | 10 +-
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 6930c63..fe4f46b 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
> >  #define KVM_REQUEST_ARCH_BASE 8
> >  
> >  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> > -   BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> > +   BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> > *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \
> > (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
> >  })
> >  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> > @@ -223,7 +223,7 @@ struct kvm_vcpu {
> > int vcpu_id;
> > int srcu_idx;
> > int mode;
> > -   unsigned long requests;
> > +   u64 requests;
> > unsigned long guest_debug;
> >  
> > int pre_pcpu;
> > @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> > kvm_vcpu *vcpu)
> >  * caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
> >  */
> > smp_wmb();
> > -   set_bit(req & KVM_REQUEST_MASK, >requests);
> > +   set_bit(req & KVM_REQUEST_MASK, (void *)>requests);
> >  }
> >  
> >  static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
> > @@ -1132,12 +1132,12 @@ static inline bool kvm_request_pending(struct 
> > kvm_vcpu *vcpu)
> >  
> >  static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
> >  {
> > -   return test_bit(req & KVM_REQUEST_MASK, >requests);
> > +   return test_bit(req & KVM_REQUEST_MASK, (void *)>requests);
> >  }
> >  
> >  static inline void kvm_clear_request(int req, struct kvm_vcpu *vcpu)
> >  {
> > -   clear_bit(req & KVM_REQUEST_MASK, >requests);
> > +   clear_bit(req & KVM_REQUEST_MASK, (void *)>requests);
> >  }
> >  
> >  static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
> > 
> 
> 
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Paolo Bonzini]

On 15/04/2018 00:26, KarimAllah Ahmed wrote:
> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> use the size of "requests" instead of the hard-coded '32'.
> 
> That gives us a bit more room again for arch-specific requests as we
> already ran out of space for x86 due to the hard-coded check.
> 
> Cc: Paolo Bonzini 
> Cc: Radim Krčmář 
> Cc: k...@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed 

I'm afraid architectures like ARM 32 need this to be conditional (using
Kconfig).

Thanks,

Paolo

> ---
>  include/linux/kvm_host.h | 10 +-
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6930c63..fe4f46b 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQUEST_ARCH_BASE 8
>  
>  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> - BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> + BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \
>   (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
>  })
>  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> @@ -223,7 +223,7 @@ struct kvm_vcpu {
>   int vcpu_id;
>   int srcu_idx;
>   int mode;
> - unsigned long requests;
> + u64 requests;
>   unsigned long guest_debug;
>  
>   int pre_pcpu;
> @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> kvm_vcpu *vcpu)
>* caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
>*/
>   smp_wmb();
> - set_bit(req & KVM_REQUEST_MASK, >requests);
> + set_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
> @@ -1132,12 +1132,12 @@ static inline bool kvm_request_pending(struct 
> kvm_vcpu *vcpu)
>  
>  static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
>  {
> - return test_bit(req & KVM_REQUEST_MASK, >requests);
> + return test_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline void kvm_clear_request(int req, struct kvm_vcpu *vcpu)
>  {
> - clear_bit(req & KVM_REQUEST_MASK, >requests);
> + clear_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
> 

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Paolo Bonzini]

On 15/04/2018 00:26, KarimAllah Ahmed wrote:
> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> use the size of "requests" instead of the hard-coded '32'.
> 
> That gives us a bit more room again for arch-specific requests as we
> already ran out of space for x86 due to the hard-coded check.
> 
> Cc: Paolo Bonzini 
> Cc: Radim Krčmář 
> Cc: k...@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed 

I'm afraid architectures like ARM 32 need this to be conditional (using
Kconfig).

Thanks,

Paolo

> ---
>  include/linux/kvm_host.h | 10 +-
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6930c63..fe4f46b 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQUEST_ARCH_BASE 8
>  
>  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> - BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> + BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \
>   (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
>  })
>  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> @@ -223,7 +223,7 @@ struct kvm_vcpu {
>   int vcpu_id;
>   int srcu_idx;
>   int mode;
> - unsigned long requests;
> + u64 requests;
>   unsigned long guest_debug;
>  
>   int pre_pcpu;
> @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> kvm_vcpu *vcpu)
>* caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
>*/
>   smp_wmb();
> - set_bit(req & KVM_REQUEST_MASK, >requests);
> + set_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
> @@ -1132,12 +1132,12 @@ static inline bool kvm_request_pending(struct 
> kvm_vcpu *vcpu)
>  
>  static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
>  {
> - return test_bit(req & KVM_REQUEST_MASK, >requests);
> + return test_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline void kvm_clear_request(int req, struct kvm_vcpu *vcpu)
>  {
> - clear_bit(req & KVM_REQUEST_MASK, >requests);
> + clear_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
> 

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Jim Mattson]

On Sun, Apr 15, 2018 at 6:12 AM, Raslan, KarimAllah  wrote:
> On Sun, 2018-04-15 at 00:26 +0200, KarimAllah Ahmed wrote:
>> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
>> use the size of "requests" instead of the hard-coded '32'.
>>
>> That gives us a bit more room again for arch-specific requests as we
>> already ran out of space for x86 due to the hard-coded check.
>>
>> Cc: Paolo Bonzini 
>> Cc: Radim Krčmář 
>> Cc: k...@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: KarimAllah Ahmed 

I like it!

Reviewed-by: Jim Mattson 

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Jim Mattson]

On Sun, Apr 15, 2018 at 6:12 AM, Raslan, KarimAllah  wrote:
> On Sun, 2018-04-15 at 00:26 +0200, KarimAllah Ahmed wrote:
>> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
>> use the size of "requests" instead of the hard-coded '32'.
>>
>> That gives us a bit more room again for arch-specific requests as we
>> already ran out of space for x86 due to the hard-coded check.
>>
>> Cc: Paolo Bonzini 
>> Cc: Radim Krčmář 
>> Cc: k...@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: KarimAllah Ahmed 

I like it!

Reviewed-by: Jim Mattson 

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Raslan, KarimAllah]

On Sun, 2018-04-15 at 00:26 +0200, KarimAllah Ahmed wrote:
> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> use the size of "requests" instead of the hard-coded '32'.
> 
> That gives us a bit more room again for arch-specific requests as we
> already ran out of space for x86 due to the hard-coded check.
> 
> Cc: Paolo Bonzini 
> Cc: Radim Krčmář 
> Cc: k...@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed 
> ---
>  include/linux/kvm_host.h | 10 +-
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6930c63..fe4f46b 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQUEST_ARCH_BASE 8
>  
>  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> - BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> + BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \

While looking at a completely unrelated code I realize that there 
is FIELD_SIZEOF that is doing exactly what I did. Will use it in v2.

>   (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
>  })
>  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> @@ -223,7 +223,7 @@ struct kvm_vcpu {
>   int vcpu_id;
>   int srcu_idx;
>   int mode;
> - unsigned long requests;
> + u64 requests;
>   unsigned long guest_debug;
>  
>   int pre_pcpu;
> @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> kvm_vcpu *vcpu)
>* caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
>*/
>   smp_wmb();
> - set_bit(req & KVM_REQUEST_MASK, >requests);
> + set_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
> @@ -1132,12 +1132,12 @@ static inline bool kvm_request_pending(struct 
> kvm_vcpu *vcpu)
>  
>  static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
>  {
> - return test_bit(req & KVM_REQUEST_MASK, >requests);
> + return test_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline void kvm_clear_request(int req, struct kvm_vcpu *vcpu)
>  {
> - clear_bit(req & KVM_REQUEST_MASK, >requests);
> + clear_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

[Raslan, KarimAllah]

On Sun, 2018-04-15 at 00:26 +0200, KarimAllah Ahmed wrote:
> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> use the size of "requests" instead of the hard-coded '32'.
> 
> That gives us a bit more room again for arch-specific requests as we
> already ran out of space for x86 due to the hard-coded check.
> 
> Cc: Paolo Bonzini 
> Cc: Radim Krčmář 
> Cc: k...@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed 
> ---
>  include/linux/kvm_host.h | 10 +-
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6930c63..fe4f46b 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQUEST_ARCH_BASE 8
>  
>  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> - BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> + BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu 
> *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \

While looking at a completely unrelated code I realize that there 
is FIELD_SIZEOF that is doing exactly what I did. Will use it in v2.

>   (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
>  })
>  #define KVM_ARCH_REQ(nr)   KVM_ARCH_REQ_FLAGS(nr, 0)
> @@ -223,7 +223,7 @@ struct kvm_vcpu {
>   int vcpu_id;
>   int srcu_idx;
>   int mode;
> - unsigned long requests;
> + u64 requests;
>   unsigned long guest_debug;
>  
>   int pre_pcpu;
> @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct 
> kvm_vcpu *vcpu)
>* caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
>*/
>   smp_wmb();
> - set_bit(req & KVM_REQUEST_MASK, >requests);
> + set_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
> @@ -1132,12 +1132,12 @@ static inline bool kvm_request_pending(struct 
> kvm_vcpu *vcpu)
>  
>  static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
>  {
> - return test_bit(req & KVM_REQUEST_MASK, >requests);
> + return test_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline void kvm_clear_request(int req, struct kvm_vcpu *vcpu)
>  {
> - clear_bit(req & KVM_REQUEST_MASK, >requests);
> + clear_bit(req & KVM_REQUEST_MASK, (void *)>requests);
>  }
>  
>  static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B