Re: [Qemu-devel] [PATCH] ppc/kvm: use kvm_vm_check_extension() in kvmppc_is_pr()

[David Gibson]

On Thu, Sep 14, 2017 at 12:48:04PM +0200, Greg Kurz wrote:
> If the host has both KVM PR and KVM HV loaded and we pass:
> 
>   -machine pseries,accel=kvm,kvm-type=PR
> 
> the kvmppc_is_pr() returns false instead of true. Since the helper
> is mostly used as fallback, it doesn't have any real impact with
> recent kernels. A notable exception is the workaround to allow
> migration between compatible hosts with different PVRs (eg, POWER8
> and POWER8E), since KVM still doesn't provide a way to check if a
> specific PVR is supported (see commit c363a37a450f for details).
> 
> According to the official KVM API documentation [1], KVM_PPC_GET_PVINFO
> is "vm ioctl", but we check it as a global ioctl. The following function
> in KVM is hence called with kvm == NULL and considers we're in HV mode.
> 
> int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> {
>   int r;
>   /* Assume we're using HV mode when the HV module is loaded */
>   int hv_enabled = kvmppc_hv_ops ? 1 : 0;
> 
>   if (kvm) {
>   /*
>* Hooray - we know which VM type we're running on. Depend on
>* that rather than the guess above.
>*/
>   hv_enabled = is_kvmppc_hv_enabled(kvm);
>   }
> 
> Let's use kvm_vm_check_extension() to fix the issue.
> 
> [1] https://www.kernel.org/doc/Documentation/virtual/kvm/api.txt
> 
> Signed-off-by: Greg Kurz 

Applied to ppc-for-2.11, good catch.

> ---
>  target/ppc/kvm.c |2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 6442dfcb95b3..1deaf106d2b9 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -120,7 +120,7 @@ static void kvm_kick_cpu(void *opaque)
>  static bool kvmppc_is_pr(KVMState *ks)
>  {
>  /* Assume KVM-PR if the GET_PVINFO capability is available */
> -return kvm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
> +return kvm_vm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
>  }
>  
>  static int kvm_ppc_register_host_cpu_type(void);
> 

-- 
David Gibson| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson


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Re: [Qemu-devel] [PATCH] ppc/kvm: use kvm_vm_check_extension() in kvmppc_is_pr()

[Greg Kurz]

On Thu, 14 Sep 2017 13:17:48 +0200
Thomas Huth  wrote:

> On 14.09.2017 12:48, Greg Kurz wrote:
> > If the host has both KVM PR and KVM HV loaded and we pass:
> > 
> > -machine pseries,accel=kvm,kvm-type=PR
> > 
> > the kvmppc_is_pr() returns false instead of true. Since the helper
> > is mostly used as fallback, it doesn't have any real impact with
> > recent kernels. A notable exception is the workaround to allow
> > migration between compatible hosts with different PVRs (eg, POWER8
> > and POWER8E), since KVM still doesn't provide a way to check if a
> > specific PVR is supported (see commit c363a37a450f for details).
> > 
> > According to the official KVM API documentation [1], KVM_PPC_GET_PVINFO
> > is "vm ioctl", but we check it as a global ioctl. The following function
> > in KVM is hence called with kvm == NULL and considers we're in HV mode.
> > 
> > int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> > {
> > int r;
> > /* Assume we're using HV mode when the HV module is loaded */
> > int hv_enabled = kvmppc_hv_ops ? 1 : 0;
> > 
> > if (kvm) {
> > /*
> >  * Hooray - we know which VM type we're running on. Depend on
> >  * that rather than the guess above.
> >  */
> > hv_enabled = is_kvmppc_hv_enabled(kvm);
> > }
> > 
> > Let's use kvm_vm_check_extension() to fix the issue.  
> 
> By the way, what about the other CAPs that rely on hv_enabled? grepping
> through the QEMU sources, I can see:
> 
>  cap_ppc_smt = kvm_check_extension(s, KVM_CAP_PPC_SMT);
> 
>  cap_htab_fd = kvm_check_extension(s, KVM_CAP_PPC_HTAB_FD);
> 
>  int ret = kvm_check_extension(s, KVM_CAP_NR_VCPUS);
> 
>  return kvm_check_extension(kvm_state, KVM_CAP_SYNC_MMU);
> 
>  !kvm_check_extension(cs->kvm_state, KVM_CAP_SW_TLB)) {
> 
> ... do we need to fix them, too?
> 

I'm currently going through the KVM code to see which ones need to be
fixed. I'll send more patches shortly :)

Cheers,

--
Greg

>  Thomas



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Re: [Qemu-devel] [PATCH] ppc/kvm: use kvm_vm_check_extension() in kvmppc_is_pr()

[Thomas Huth]

On 14.09.2017 12:48, Greg Kurz wrote:
> If the host has both KVM PR and KVM HV loaded and we pass:
> 
>   -machine pseries,accel=kvm,kvm-type=PR
> 
> the kvmppc_is_pr() returns false instead of true. Since the helper
> is mostly used as fallback, it doesn't have any real impact with
> recent kernels. A notable exception is the workaround to allow
> migration between compatible hosts with different PVRs (eg, POWER8
> and POWER8E), since KVM still doesn't provide a way to check if a
> specific PVR is supported (see commit c363a37a450f for details).
> 
> According to the official KVM API documentation [1], KVM_PPC_GET_PVINFO
> is "vm ioctl", but we check it as a global ioctl. The following function
> in KVM is hence called with kvm == NULL and considers we're in HV mode.
> 
> int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> {
>   int r;
>   /* Assume we're using HV mode when the HV module is loaded */
>   int hv_enabled = kvmppc_hv_ops ? 1 : 0;
> 
>   if (kvm) {
>   /*
>* Hooray - we know which VM type we're running on. Depend on
>* that rather than the guess above.
>*/
>   hv_enabled = is_kvmppc_hv_enabled(kvm);
>   }
> 
> Let's use kvm_vm_check_extension() to fix the issue.

By the way, what about the other CAPs that rely on hv_enabled? grepping
through the QEMU sources, I can see:

 cap_ppc_smt = kvm_check_extension(s, KVM_CAP_PPC_SMT);

 cap_htab_fd = kvm_check_extension(s, KVM_CAP_PPC_HTAB_FD);

 int ret = kvm_check_extension(s, KVM_CAP_NR_VCPUS);

 return kvm_check_extension(kvm_state, KVM_CAP_SYNC_MMU);

 !kvm_check_extension(cs->kvm_state, KVM_CAP_SW_TLB)) {

... do we need to fix them, too?

 Thomas

Re: [Qemu-devel] [PATCH] ppc/kvm: use kvm_vm_check_extension() in kvmppc_is_pr()

[Thomas Huth]

On 14.09.2017 12:48, Greg Kurz wrote:
> If the host has both KVM PR and KVM HV loaded and we pass:
> 
>   -machine pseries,accel=kvm,kvm-type=PR
> 
> the kvmppc_is_pr() returns false instead of true. Since the helper
> is mostly used as fallback, it doesn't have any real impact with
> recent kernels. A notable exception is the workaround to allow
> migration between compatible hosts with different PVRs (eg, POWER8
> and POWER8E), since KVM still doesn't provide a way to check if a
> specific PVR is supported (see commit c363a37a450f for details).
> 
> According to the official KVM API documentation [1], KVM_PPC_GET_PVINFO
> is "vm ioctl", but we check it as a global ioctl. The following function
> in KVM is hence called with kvm == NULL and considers we're in HV mode.
> 
> int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> {
>   int r;
>   /* Assume we're using HV mode when the HV module is loaded */
>   int hv_enabled = kvmppc_hv_ops ? 1 : 0;
> 
>   if (kvm) {
>   /*
>* Hooray - we know which VM type we're running on. Depend on
>* that rather than the guess above.
>*/
>   hv_enabled = is_kvmppc_hv_enabled(kvm);
>   }
> 
> Let's use kvm_vm_check_extension() to fix the issue.
> 
> [1] https://www.kernel.org/doc/Documentation/virtual/kvm/api.txt
> 
> Signed-off-by: Greg Kurz 
> ---
>  target/ppc/kvm.c |2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 6442dfcb95b3..1deaf106d2b9 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -120,7 +120,7 @@ static void kvm_kick_cpu(void *opaque)
>  static bool kvmppc_is_pr(KVMState *ks)
>  {
>  /* Assume KVM-PR if the GET_PVINFO capability is available */
> -return kvm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
> +return kvm_vm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
>  }
>  
>  static int kvm_ppc_register_host_cpu_type(void);
> 

Ooops, good catch!

Reviewed-by: Thomas Huth 

[Qemu-devel] [PATCH] ppc/kvm: use kvm_vm_check_extension() in kvmppc_is_pr()

[Greg Kurz]

If the host has both KVM PR and KVM HV loaded and we pass:

-machine pseries,accel=kvm,kvm-type=PR

the kvmppc_is_pr() returns false instead of true. Since the helper
is mostly used as fallback, it doesn't have any real impact with
recent kernels. A notable exception is the workaround to allow
migration between compatible hosts with different PVRs (eg, POWER8
and POWER8E), since KVM still doesn't provide a way to check if a
specific PVR is supported (see commit c363a37a450f for details).

According to the official KVM API documentation [1], KVM_PPC_GET_PVINFO
is "vm ioctl", but we check it as a global ioctl. The following function
in KVM is hence called with kvm == NULL and considers we're in HV mode.

int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
{
int r;
/* Assume we're using HV mode when the HV module is loaded */
int hv_enabled = kvmppc_hv_ops ? 1 : 0;

if (kvm) {
/*
 * Hooray - we know which VM type we're running on. Depend on
 * that rather than the guess above.
 */
hv_enabled = is_kvmppc_hv_enabled(kvm);
}

Let's use kvm_vm_check_extension() to fix the issue.

[1] https://www.kernel.org/doc/Documentation/virtual/kvm/api.txt

Signed-off-by: Greg Kurz 
---
 target/ppc/kvm.c |2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 6442dfcb95b3..1deaf106d2b9 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -120,7 +120,7 @@ static void kvm_kick_cpu(void *opaque)
 static bool kvmppc_is_pr(KVMState *ks)
 {
 /* Assume KVM-PR if the GET_PVINFO capability is available */
-return kvm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
+return kvm_vm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
 }
 
 static int kvm_ppc_register_host_cpu_type(void);