Re: [RFC v3 1/2] x86/xen: add xen_is_preemptible_hypercall()
On Thu, Jan 22, 2015 at 09:44:12PM +, Andrew Cooper wrote:
> On 22/01/2015 21:09, Luis R. Rodriguez wrote:
> > On Thu, Jan 22, 2015 at 12:01:50PM -0800, Andy Lutomirski wrote:
> >> On Thu, Jan 22, 2015 at 11:30 AM, Luis R. Rodriguez
> >> wrote:
> >>> On Wed, Jan 21, 2015 at 07:07:36PM -0800, Andy Lutomirski wrote:
> On Wed, Jan 21, 2015 at 6:17 PM, Luis R. Rodriguez
> wrote:
> > From: "Luis R. Rodriguez"
> >
> > On kernels with voluntary or no preemption we can run
> > into situations where a hypercall issued through userspace
> > will linger around as it addresses sub-operatiosn in kernel
> > context (multicalls). Such operations can trigger soft lockup
> > detection.
> >
> > We want to address a way to let the kernel voluntarily preempt
> > such calls even on non preempt kernels, to address this we first
> > need to distinguish which hypercalls fall under this category.
> > This implements xen_is_preemptible_hypercall() which lets us do
> > just that by adding a secondary hypercall page, calls made via
> > the new page may be preempted.
> >
> > Andrew had originally submitted a version of this work [0].
> >
> > [0] http://lists.xen.org/archives/html/xen-devel/2014-02/msg01056.html
> >
> > Based on original work by: Andrew Cooper
> >
> > Cc: Andy Lutomirski
> > Cc: Borislav Petkov
> > Cc: David Vrabel
> > Cc: Thomas Gleixner
> > Cc: Ingo Molnar
> > Cc: "H. Peter Anvin"
> > Cc: x...@kernel.org
> > Cc: Steven Rostedt
> > Cc: Masami Hiramatsu
> > Cc: Jan Beulich
> > Cc: linux-ker...@vger.kernel.org
> > Signed-off-by: Luis R. Rodriguez
> > ---
> > arch/x86/include/asm/xen/hypercall.h | 20
> > arch/x86/xen/enlighten.c | 7 +++
> > arch/x86/xen/xen-head.S | 18 +-
> > 3 files changed, 44 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/include/asm/xen/hypercall.h
> > b/arch/x86/include/asm/xen/hypercall.h
> > index ca08a27..221008e 100644
> > --- a/arch/x86/include/asm/xen/hypercall.h
> > +++ b/arch/x86/include/asm/xen/hypercall.h
> > @@ -84,6 +84,22 @@
> >
> > extern struct { char _entry[32]; } hypercall_page[];
> >
> > +#ifndef CONFIG_PREEMPT
> > +extern struct { char _entry[32]; } preemptible_hypercall_page[];
> A comment somewhere explaining why only non-preemptible kernels have
> preemptible hypercalls might be friendly to some future reader. :)
> >>> Good idea, since this section is arch specific, I'll instead add a blurb
> >>> explaining this on the upcall.
> >>>
> > +
> > +static inline bool xen_is_preemptible_hypercall(struct pt_regs *regs)
> > +{
> > + return !user_mode_vm(regs) &&
> > + regs->ip >= (unsigned long)preemptible_hypercall_page &&
> > + regs->ip < (unsigned long)preemptible_hypercall_page +
> > PAGE_SIZE;
> > +}
> This makes it seem like the page is indeed one page long, but I don't
> see what actually allocates a whole page for it. What am I missing?
> >>> arch/x86/xen/xen-head.S
> >>>
> >>> .pushsection .text
> >>> .balign PAGE_SIZE
> >>> ENTRY(hypercall_page)
> >>>
> >>> #ifndef CONFIG_PREEMPT
> >>> ENTRY(preemptible_hypercall_page)
> >>> .skip PAGE_SIZE
> >>> #endif /* CONFIG_PREEMPT */
> >>>
> >>> Does that suffice to be sure?
> >> This looks like hypercall_page and preemptible_hypercall_page will
> >> both be page-aligned but will be the same page. Should there be
> >> another .skip PAGE_SIZE in there?
> > I think the trick here was since hypercall_page is already aligned,
> > and we are just allocation PAGE_SIZE we are essentially pegging
> > preemptible_hypercall_page right after hypercall_page.
> >
> > Andrew, David, can you confirm?
>
> Your version is different to my original one (observe the lack of
> NEXT_HYPERCALL()s),
I don't get what is missing they should be pretty identical. It had:
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -85,9 +85,18 @@ ENTRY(xen_pvh_early_cpu_init)
.pushsection .text
.balign PAGE_SIZE
ENTRY(hypercall_page)
+
+#ifdef CONFIG_PREEMPT
+# define PREEMPT_HYPERCALL_ENTRY(x)
+#else
+# define PREEMPT_HYPERCALL_ENTRY(x) \
+ .global xen_hypercall_##x ## _p ASM_NL \
+ .set preemptible_xen_hypercall_##x, xen_hypercall_##x + PAGE_SIZE ASM_NL
+#endif
#define NEXT_HYPERCALL(x) \
ENTRY(xen_hypercall_##x) \
- .skip 32
+ .skip 32 ASM_NL \
+ PREEMPT_HYPERCALL_ENTRY(x)
Is that what you mean?
> and I would agree that it would appear as if in your
> version, hypercall_page and preemptible_hypercall_page are symbols with
> the same address.
>
> nm should give you a quick confirmation one way or another.
symtab:
mcgrof@ergon ~/linux (git::hypercall-preemption-v3)$ grep hypercall_page
/boo
Re: [RFC v3 1/2] x86/xen: add xen_is_preemptible_hypercall()
On 22/01/2015 21:09, Luis R. Rodriguez wrote:
> On Thu, Jan 22, 2015 at 12:01:50PM -0800, Andy Lutomirski wrote:
>> On Thu, Jan 22, 2015 at 11:30 AM, Luis R. Rodriguez wrote:
>>> On Wed, Jan 21, 2015 at 07:07:36PM -0800, Andy Lutomirski wrote:
On Wed, Jan 21, 2015 at 6:17 PM, Luis R. Rodriguez
wrote:
> From: "Luis R. Rodriguez"
>
> On kernels with voluntary or no preemption we can run
> into situations where a hypercall issued through userspace
> will linger around as it addresses sub-operatiosn in kernel
> context (multicalls). Such operations can trigger soft lockup
> detection.
>
> We want to address a way to let the kernel voluntarily preempt
> such calls even on non preempt kernels, to address this we first
> need to distinguish which hypercalls fall under this category.
> This implements xen_is_preemptible_hypercall() which lets us do
> just that by adding a secondary hypercall page, calls made via
> the new page may be preempted.
>
> Andrew had originally submitted a version of this work [0].
>
> [0] http://lists.xen.org/archives/html/xen-devel/2014-02/msg01056.html
>
> Based on original work by: Andrew Cooper
>
> Cc: Andy Lutomirski
> Cc: Borislav Petkov
> Cc: David Vrabel
> Cc: Thomas Gleixner
> Cc: Ingo Molnar
> Cc: "H. Peter Anvin"
> Cc: x...@kernel.org
> Cc: Steven Rostedt
> Cc: Masami Hiramatsu
> Cc: Jan Beulich
> Cc: linux-ker...@vger.kernel.org
> Signed-off-by: Luis R. Rodriguez
> ---
> arch/x86/include/asm/xen/hypercall.h | 20
> arch/x86/xen/enlighten.c | 7 +++
> arch/x86/xen/xen-head.S | 18 +-
> 3 files changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/xen/hypercall.h
> b/arch/x86/include/asm/xen/hypercall.h
> index ca08a27..221008e 100644
> --- a/arch/x86/include/asm/xen/hypercall.h
> +++ b/arch/x86/include/asm/xen/hypercall.h
> @@ -84,6 +84,22 @@
>
> extern struct { char _entry[32]; } hypercall_page[];
>
> +#ifndef CONFIG_PREEMPT
> +extern struct { char _entry[32]; } preemptible_hypercall_page[];
A comment somewhere explaining why only non-preemptible kernels have
preemptible hypercalls might be friendly to some future reader. :)
>>> Good idea, since this section is arch specific, I'll instead add a blurb
>>> explaining this on the upcall.
>>>
> +
> +static inline bool xen_is_preemptible_hypercall(struct pt_regs *regs)
> +{
> + return !user_mode_vm(regs) &&
> + regs->ip >= (unsigned long)preemptible_hypercall_page &&
> + regs->ip < (unsigned long)preemptible_hypercall_page +
> PAGE_SIZE;
> +}
This makes it seem like the page is indeed one page long, but I don't
see what actually allocates a whole page for it. What am I missing?
>>> arch/x86/xen/xen-head.S
>>>
>>> .pushsection .text
>>> .balign PAGE_SIZE
>>> ENTRY(hypercall_page)
>>>
>>> #ifndef CONFIG_PREEMPT
>>> ENTRY(preemptible_hypercall_page)
>>> .skip PAGE_SIZE
>>> #endif /* CONFIG_PREEMPT */
>>>
>>> Does that suffice to be sure?
>> This looks like hypercall_page and preemptible_hypercall_page will
>> both be page-aligned but will be the same page. Should there be
>> another .skip PAGE_SIZE in there?
> I think the trick here was since hypercall_page is already aligned,
> and we are just allocation PAGE_SIZE we are essentially pegging
> preemptible_hypercall_page right after hypercall_page.
>
> Andrew, David, can you confirm?
Your version is different to my original one (observe the lack of
NEXT_HYPERCALL()s), and I would agree that it would appear as if in your
version, hypercall_page and preemptible_hypercall_page are symbols with
the same address.
nm should give you a quick confirmation one way or another.
~Andrew
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Re: [RFC v3 1/2] x86/xen: add xen_is_preemptible_hypercall()
On Thu, Jan 22, 2015 at 12:01:50PM -0800, Andy Lutomirski wrote:
> On Thu, Jan 22, 2015 at 11:30 AM, Luis R. Rodriguez wrote:
> > On Wed, Jan 21, 2015 at 07:07:36PM -0800, Andy Lutomirski wrote:
> >> On Wed, Jan 21, 2015 at 6:17 PM, Luis R. Rodriguez
> >> wrote:
> >> > From: "Luis R. Rodriguez"
> >> >
> >> > On kernels with voluntary or no preemption we can run
> >> > into situations where a hypercall issued through userspace
> >> > will linger around as it addresses sub-operatiosn in kernel
> >> > context (multicalls). Such operations can trigger soft lockup
> >> > detection.
> >> >
> >> > We want to address a way to let the kernel voluntarily preempt
> >> > such calls even on non preempt kernels, to address this we first
> >> > need to distinguish which hypercalls fall under this category.
> >> > This implements xen_is_preemptible_hypercall() which lets us do
> >> > just that by adding a secondary hypercall page, calls made via
> >> > the new page may be preempted.
> >> >
> >> > Andrew had originally submitted a version of this work [0].
> >> >
> >> > [0] http://lists.xen.org/archives/html/xen-devel/2014-02/msg01056.html
> >> >
> >> > Based on original work by: Andrew Cooper
> >> >
> >> > Cc: Andy Lutomirski
> >> > Cc: Borislav Petkov
> >> > Cc: David Vrabel
> >> > Cc: Thomas Gleixner
> >> > Cc: Ingo Molnar
> >> > Cc: "H. Peter Anvin"
> >> > Cc: x...@kernel.org
> >> > Cc: Steven Rostedt
> >> > Cc: Masami Hiramatsu
> >> > Cc: Jan Beulich
> >> > Cc: linux-ker...@vger.kernel.org
> >> > Signed-off-by: Luis R. Rodriguez
> >> > ---
> >> > arch/x86/include/asm/xen/hypercall.h | 20
> >> > arch/x86/xen/enlighten.c | 7 +++
> >> > arch/x86/xen/xen-head.S | 18 +-
> >> > 3 files changed, 44 insertions(+), 1 deletion(-)
> >> >
> >> > diff --git a/arch/x86/include/asm/xen/hypercall.h
> >> > b/arch/x86/include/asm/xen/hypercall.h
> >> > index ca08a27..221008e 100644
> >> > --- a/arch/x86/include/asm/xen/hypercall.h
> >> > +++ b/arch/x86/include/asm/xen/hypercall.h
> >> > @@ -84,6 +84,22 @@
> >> >
> >> > extern struct { char _entry[32]; } hypercall_page[];
> >> >
> >> > +#ifndef CONFIG_PREEMPT
> >> > +extern struct { char _entry[32]; } preemptible_hypercall_page[];
> >>
> >> A comment somewhere explaining why only non-preemptible kernels have
> >> preemptible hypercalls might be friendly to some future reader. :)
> >
> > Good idea, since this section is arch specific, I'll instead add a blurb
> > explaining this on the upcall.
> >
> >> > +
> >> > +static inline bool xen_is_preemptible_hypercall(struct pt_regs *regs)
> >> > +{
> >> > + return !user_mode_vm(regs) &&
> >> > + regs->ip >= (unsigned long)preemptible_hypercall_page &&
> >> > + regs->ip < (unsigned long)preemptible_hypercall_page +
> >> > PAGE_SIZE;
> >> > +}
> >>
> >> This makes it seem like the page is indeed one page long, but I don't
> >> see what actually allocates a whole page for it. What am I missing?
> >
> > arch/x86/xen/xen-head.S
> >
> > .pushsection .text
> > .balign PAGE_SIZE
> > ENTRY(hypercall_page)
> >
> > #ifndef CONFIG_PREEMPT
> > ENTRY(preemptible_hypercall_page)
> > .skip PAGE_SIZE
> > #endif /* CONFIG_PREEMPT */
> >
> > Does that suffice to be sure?
>
> This looks like hypercall_page and preemptible_hypercall_page will
> both be page-aligned but will be the same page. Should there be
> another .skip PAGE_SIZE in there?
I think the trick here was since hypercall_page is already aligned,
and we are just allocation PAGE_SIZE we are essentially pegging
preemptible_hypercall_page right after hypercall_page.
Andrew, David, can you confirm?
Luis
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Re: [RFC v3 1/2] x86/xen: add xen_is_preemptible_hypercall()
On Thu, Jan 22, 2015 at 11:30 AM, Luis R. Rodriguez wrote:
> On Wed, Jan 21, 2015 at 07:07:36PM -0800, Andy Lutomirski wrote:
>> On Wed, Jan 21, 2015 at 6:17 PM, Luis R. Rodriguez
>> wrote:
>> > From: "Luis R. Rodriguez"
>> >
>> > On kernels with voluntary or no preemption we can run
>> > into situations where a hypercall issued through userspace
>> > will linger around as it addresses sub-operatiosn in kernel
>> > context (multicalls). Such operations can trigger soft lockup
>> > detection.
>> >
>> > We want to address a way to let the kernel voluntarily preempt
>> > such calls even on non preempt kernels, to address this we first
>> > need to distinguish which hypercalls fall under this category.
>> > This implements xen_is_preemptible_hypercall() which lets us do
>> > just that by adding a secondary hypercall page, calls made via
>> > the new page may be preempted.
>> >
>> > Andrew had originally submitted a version of this work [0].
>> >
>> > [0] http://lists.xen.org/archives/html/xen-devel/2014-02/msg01056.html
>> >
>> > Based on original work by: Andrew Cooper
>> >
>> > Cc: Andy Lutomirski
>> > Cc: Borislav Petkov
>> > Cc: David Vrabel
>> > Cc: Thomas Gleixner
>> > Cc: Ingo Molnar
>> > Cc: "H. Peter Anvin"
>> > Cc: x...@kernel.org
>> > Cc: Steven Rostedt
>> > Cc: Masami Hiramatsu
>> > Cc: Jan Beulich
>> > Cc: linux-ker...@vger.kernel.org
>> > Signed-off-by: Luis R. Rodriguez
>> > ---
>> > arch/x86/include/asm/xen/hypercall.h | 20
>> > arch/x86/xen/enlighten.c | 7 +++
>> > arch/x86/xen/xen-head.S | 18 +-
>> > 3 files changed, 44 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/arch/x86/include/asm/xen/hypercall.h
>> > b/arch/x86/include/asm/xen/hypercall.h
>> > index ca08a27..221008e 100644
>> > --- a/arch/x86/include/asm/xen/hypercall.h
>> > +++ b/arch/x86/include/asm/xen/hypercall.h
>> > @@ -84,6 +84,22 @@
>> >
>> > extern struct { char _entry[32]; } hypercall_page[];
>> >
>> > +#ifndef CONFIG_PREEMPT
>> > +extern struct { char _entry[32]; } preemptible_hypercall_page[];
>>
>> A comment somewhere explaining why only non-preemptible kernels have
>> preemptible hypercalls might be friendly to some future reader. :)
>
> Good idea, since this section is arch specific, I'll instead add a blurb
> explaining this on the upcall.
>
>> > +
>> > +static inline bool xen_is_preemptible_hypercall(struct pt_regs *regs)
>> > +{
>> > + return !user_mode_vm(regs) &&
>> > + regs->ip >= (unsigned long)preemptible_hypercall_page &&
>> > + regs->ip < (unsigned long)preemptible_hypercall_page +
>> > PAGE_SIZE;
>> > +}
>>
>> This makes it seem like the page is indeed one page long, but I don't
>> see what actually allocates a whole page for it. What am I missing?
>
> arch/x86/xen/xen-head.S
>
> .pushsection .text
> .balign PAGE_SIZE
> ENTRY(hypercall_page)
>
> #ifndef CONFIG_PREEMPT
> ENTRY(preemptible_hypercall_page)
> .skip PAGE_SIZE
> #endif /* CONFIG_PREEMPT */
>
> Does that suffice to be sure?
This looks like hypercall_page and preemptible_hypercall_page will
both be page-aligned but will be the same page. Should there be
another .skip PAGE_SIZE in there?
--Andy
>
> Luis
--
Andy Lutomirski
AMA Capital Management, LLC
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Re: [RFC v3 1/2] x86/xen: add xen_is_preemptible_hypercall()
On Wed, Jan 21, 2015 at 07:07:36PM -0800, Andy Lutomirski wrote:
> On Wed, Jan 21, 2015 at 6:17 PM, Luis R. Rodriguez
> wrote:
> > From: "Luis R. Rodriguez"
> >
> > On kernels with voluntary or no preemption we can run
> > into situations where a hypercall issued through userspace
> > will linger around as it addresses sub-operatiosn in kernel
> > context (multicalls). Such operations can trigger soft lockup
> > detection.
> >
> > We want to address a way to let the kernel voluntarily preempt
> > such calls even on non preempt kernels, to address this we first
> > need to distinguish which hypercalls fall under this category.
> > This implements xen_is_preemptible_hypercall() which lets us do
> > just that by adding a secondary hypercall page, calls made via
> > the new page may be preempted.
> >
> > Andrew had originally submitted a version of this work [0].
> >
> > [0] http://lists.xen.org/archives/html/xen-devel/2014-02/msg01056.html
> >
> > Based on original work by: Andrew Cooper
> >
> > Cc: Andy Lutomirski
> > Cc: Borislav Petkov
> > Cc: David Vrabel
> > Cc: Thomas Gleixner
> > Cc: Ingo Molnar
> > Cc: "H. Peter Anvin"
> > Cc: x...@kernel.org
> > Cc: Steven Rostedt
> > Cc: Masami Hiramatsu
> > Cc: Jan Beulich
> > Cc: linux-ker...@vger.kernel.org
> > Signed-off-by: Luis R. Rodriguez
> > ---
> > arch/x86/include/asm/xen/hypercall.h | 20
> > arch/x86/xen/enlighten.c | 7 +++
> > arch/x86/xen/xen-head.S | 18 +-
> > 3 files changed, 44 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/include/asm/xen/hypercall.h
> > b/arch/x86/include/asm/xen/hypercall.h
> > index ca08a27..221008e 100644
> > --- a/arch/x86/include/asm/xen/hypercall.h
> > +++ b/arch/x86/include/asm/xen/hypercall.h
> > @@ -84,6 +84,22 @@
> >
> > extern struct { char _entry[32]; } hypercall_page[];
> >
> > +#ifndef CONFIG_PREEMPT
> > +extern struct { char _entry[32]; } preemptible_hypercall_page[];
>
> A comment somewhere explaining why only non-preemptible kernels have
> preemptible hypercalls might be friendly to some future reader. :)
Good idea, since this section is arch specific, I'll instead add a blurb
explaining this on the upcall.
> > +
> > +static inline bool xen_is_preemptible_hypercall(struct pt_regs *regs)
> > +{
> > + return !user_mode_vm(regs) &&
> > + regs->ip >= (unsigned long)preemptible_hypercall_page &&
> > + regs->ip < (unsigned long)preemptible_hypercall_page +
> > PAGE_SIZE;
> > +}
>
> This makes it seem like the page is indeed one page long, but I don't
> see what actually allocates a whole page for it. What am I missing?
arch/x86/xen/xen-head.S
.pushsection .text
.balign PAGE_SIZE
ENTRY(hypercall_page)
#ifndef CONFIG_PREEMPT
ENTRY(preemptible_hypercall_page)
.skip PAGE_SIZE
#endif /* CONFIG_PREEMPT */
Does that suffice to be sure?
Luis
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Re: [RFC v3 1/2] x86/xen: add xen_is_preemptible_hypercall()
On Wed, Jan 21, 2015 at 6:17 PM, Luis R. Rodriguez
wrote:
> From: "Luis R. Rodriguez"
>
> On kernels with voluntary or no preemption we can run
> into situations where a hypercall issued through userspace
> will linger around as it addresses sub-operatiosn in kernel
> context (multicalls). Such operations can trigger soft lockup
> detection.
>
> We want to address a way to let the kernel voluntarily preempt
> such calls even on non preempt kernels, to address this we first
> need to distinguish which hypercalls fall under this category.
> This implements xen_is_preemptible_hypercall() which lets us do
> just that by adding a secondary hypercall page, calls made via
> the new page may be preempted.
>
> Andrew had originally submitted a version of this work [0].
>
> [0] http://lists.xen.org/archives/html/xen-devel/2014-02/msg01056.html
>
> Based on original work by: Andrew Cooper
>
> Cc: Andy Lutomirski
> Cc: Borislav Petkov
> Cc: David Vrabel
> Cc: Thomas Gleixner
> Cc: Ingo Molnar
> Cc: "H. Peter Anvin"
> Cc: x...@kernel.org
> Cc: Steven Rostedt
> Cc: Masami Hiramatsu
> Cc: Jan Beulich
> Cc: linux-ker...@vger.kernel.org
> Signed-off-by: Luis R. Rodriguez
> ---
> arch/x86/include/asm/xen/hypercall.h | 20
> arch/x86/xen/enlighten.c | 7 +++
> arch/x86/xen/xen-head.S | 18 +-
> 3 files changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/xen/hypercall.h
> b/arch/x86/include/asm/xen/hypercall.h
> index ca08a27..221008e 100644
> --- a/arch/x86/include/asm/xen/hypercall.h
> +++ b/arch/x86/include/asm/xen/hypercall.h
> @@ -84,6 +84,22 @@
>
> extern struct { char _entry[32]; } hypercall_page[];
>
> +#ifndef CONFIG_PREEMPT
> +extern struct { char _entry[32]; } preemptible_hypercall_page[];
A comment somewhere explaining why only non-preemptible kernels have
preemptible hypercalls might be friendly to some future reader. :)
> +
> +static inline bool xen_is_preemptible_hypercall(struct pt_regs *regs)
> +{
> + return !user_mode_vm(regs) &&
> + regs->ip >= (unsigned long)preemptible_hypercall_page &&
> + regs->ip < (unsigned long)preemptible_hypercall_page +
> PAGE_SIZE;
> +}
This makes it seem like the page is indeed one page long, but I don't
see what actually allocates a whole page for it. What am I missing?
--Andy
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