On 21/04/2015 09:52, Paolo Bonzini wrote:
> From: Nadav Amit <[email protected]>
>
> [ upstream commit f210f7572bedf3320599e8b2d8e8ec2d96270d0b ]
>
> apic_find_highest_irr assumes irr_pending is set if any vector in APIC_IRR is
> set. If this assumption is broken and apicv is disabled, the injection of
> interrupts may be deferred until another interrupt is delivered to the guest.
> Ultimately, if no other interrupt should be injected to that vCPU, the pending
> interrupt may be lost.
>
> commit 56cc2406d68c ("KVM: nVMX: fix "acknowledge interrupt on exit" when APICv
> is in use") changed the behavior of apic_clear_irr so irr_pending is cleared
> after setting APIC_IRR vector. After this commit, if apic_set_irr and
> apic_clear_irr run simultaneously, a race may occur, resulting in APIC_IRR
> vector set, and irr_pending cleared. In the following example, assume a single
> vector is set in IRR prior to calling apic_clear_irr:
>
> apic_set_irr apic_clear_irr
> ------------ --------------
> apic->irr_pending = true;
> apic_clear_vector(...);
> vec = apic_search_irr(apic);
> // => vec == -1
> apic_set_vector(...);
> apic->irr_pending = (vec != -1);
> // => apic->irr_pending == false
>
> Nonetheless, it appears the race might even occur prior to this commit:
>
> apic_set_irr apic_clear_irr
> ------------ --------------
> apic->irr_pending = true;
> apic->irr_pending = false;
> apic_clear_vector(...);
> if (apic_search_irr(apic) != -1)
> apic->irr_pending = true;
> // => apic->irr_pending == false
> apic_set_vector(...);
>
> Fixing this issue by:
> 1. Restoring the previous behavior of apic_clear_irr: clear irr_pending, call
> apic_clear_vector, and then if APIC_IRR is non-zero, set irr_pending.
> 2. On apic_set_irr: first call apic_set_vector, then set irr_pending.
>
> Signed-off-by: Nadav Amit <[email protected]>
> Fixes: 33e4c68656a2e461b296ce714ec322978de85412
> Cc: [email protected] # 2.6.32+
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---
> The race was reported in 3.17+ by Brad Campbell and in
> 2.6.32 by Saso Slavicic, so it qualifies for stable.
Patch for kernels before 3.17:
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 6e8ce5a1a05d..e0e5642dae41 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -341,8 +341,12 @@ EXPORT_SYMBOL_GPL(kvm_apic_update_irr);
static inline void apic_set_irr(int vec, struct kvm_lapic *apic)
{
- apic->irr_pending = true;
apic_set_vector(vec, apic->regs + APIC_IRR);
+ /*
+ * irr_pending must be true if any interrupt is pending; set it after
+ * APIC_IRR to avoid race with apic_clear_irr
+ */
+ apic->irr_pending = true;
}
static inline int apic_search_irr(struct kvm_lapic *apic)
Thanks,
Paolo
On Tue, Apr 21, 2015 at 10:47:37AM +0200, Paolo Bonzini wrote:
>
>
> On 21/04/2015 09:52, Paolo Bonzini wrote:
> > From: Nadav Amit <[email protected]>
> >
> > [ upstream commit f210f7572bedf3320599e8b2d8e8ec2d96270d0b ]
> >
> > apic_find_highest_irr assumes irr_pending is set if any vector in APIC_IRR is
> > set. If this assumption is broken and apicv is disabled, the injection of
> > interrupts may be deferred until another interrupt is delivered to the guest.
> > Ultimately, if no other interrupt should be injected to that vCPU, the pending
> > interrupt may be lost.
> >
> > commit 56cc2406d68c ("KVM: nVMX: fix "acknowledge interrupt on exit" when APICv
> > is in use") changed the behavior of apic_clear_irr so irr_pending is cleared
> > after setting APIC_IRR vector. After this commit, if apic_set_irr and
> > apic_clear_irr run simultaneously, a race may occur, resulting in APIC_IRR
> > vector set, and irr_pending cleared. In the following example, assume a single
> > vector is set in IRR prior to calling apic_clear_irr:
> >
> > apic_set_irr apic_clear_irr
> > ------------ --------------
> > apic->irr_pending = true;
> > apic_clear_vector(...);
> > vec = apic_search_irr(apic);
> > // => vec == -1
> > apic_set_vector(...);
> > apic->irr_pending = (vec != -1);
> > // => apic->irr_pending == false
> >
> > Nonetheless, it appears the race might even occur prior to this commit:
> >
> > apic_set_irr apic_clear_irr
> > ------------ --------------
> > apic->irr_pending = true;
> > apic->irr_pending = false;
> > apic_clear_vector(...);
> > if (apic_search_irr(apic) != -1)
> > apic->irr_pending = true;
> > // => apic->irr_pending == false
> > apic_set_vector(...);
> >
> > Fixing this issue by:
> > 1. Restoring the previous behavior of apic_clear_irr: clear irr_pending, call
> > apic_clear_vector, and then if APIC_IRR is non-zero, set irr_pending.
> > 2. On apic_set_irr: first call apic_set_vector, then set irr_pending.
> >
> > Signed-off-by: Nadav Amit <[email protected]>
> > Fixes: 33e4c68656a2e461b296ce714ec322978de85412
> > Cc: [email protected] # 2.6.32+
> > Signed-off-by: Paolo Bonzini <[email protected]>
> > ---
> > The race was reported in 3.17+ by Brad Campbell and in
> > 2.6.32 by Saso Slavicic, so it qualifies for stable.
>
> Patch for kernels before 3.17:
>
Thanks Paolo. I was going to apply this backport to the 3.16 kernel
but it looks like the original commit is a clean cherry-pick. Shall I
still apply your backport, or do you think the original commit should
be applied instead?
Cheers,
--
Lu?s
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 6e8ce5a1a05d..e0e5642dae41 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -341,8 +341,12 @@ EXPORT_SYMBOL_GPL(kvm_apic_update_irr);
>
> static inline void apic_set_irr(int vec, struct kvm_lapic *apic)
> {
> - apic->irr_pending = true;
> apic_set_vector(vec, apic->regs + APIC_IRR);
> + /*
> + * irr_pending must be true if any interrupt is pending; set it after
> + * APIC_IRR to avoid race with apic_clear_irr
> + */
> + apic->irr_pending = true;
> }
>
> static inline int apic_search_irr(struct kvm_lapic *apic)
>
>
> Thanks,
>
> Paolo
> --
> To unsubscribe from this list: send the line "unsubscribe stable" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html
On 22/04/2015 15:34, Luis Henriques wrote:
> Thanks Paolo. I was going to apply this backport to the 3.16 kernel
> but it looks like the original commit is a clean cherry-pick. Shall I
> still apply your backport, or do you think the original commit should
> be applied instead?
Indeed you're right. I wrote the backport for 3.16(.0). However,
commit 56cc2406d68c0f09505c389e276f27a99f495cbd was marked for stable,
so it's necessary to cherry-pick the entire patch on the stable kernel
where the buggy commit was backported.
That should be, according to the [email protected] archives,
3.10.54+, 3.13.11.7+, 3.14.18+, 3.16.2+.
Paolo
> Cheers,
> --
> Lu?s
>
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> index 6e8ce5a1a05d..e0e5642dae41 100644
>> --- a/arch/x86/kvm/lapic.c
>> +++ b/arch/x86/kvm/lapic.c
>> @@ -341,8 +341,12 @@ EXPORT_SYMBOL_GPL(kvm_apic_update_irr);
>>
>> static inline void apic_set_irr(int vec, struct kvm_lapic *apic)
>> {
>> - apic->irr_pending = true;
>> apic_set_vector(vec, apic->regs + APIC_IRR);
>> + /*
>> + * irr_pending must be true if any interrupt is pending; set it after
>> + * APIC_IRR to avoid race with apic_clear_irr
>> + */
>> + apic->irr_pending = true;
>> }
>>
>> static inline int apic_search_irr(struct kvm_lapic *apic)
>>
>>
>> Thanks,
>>
>> Paolo
>> --
>> To unsubscribe from this list: send the line "unsubscribe stable" in
>> the body of a message to [email protected]
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Apr 22, 2015 at 03:47:04PM +0200, Paolo Bonzini wrote:
>
>
> On 22/04/2015 15:34, Luis Henriques wrote:
> > Thanks Paolo. I was going to apply this backport to the 3.16 kernel
> > but it looks like the original commit is a clean cherry-pick. Shall I
> > still apply your backport, or do you think the original commit should
> > be applied instead?
>
> Indeed you're right. I wrote the backport for 3.16(.0). However,
> commit 56cc2406d68c0f09505c389e276f27a99f495cbd was marked for stable,
> so it's necessary to cherry-pick the entire patch on the stable kernel
> where the buggy commit was backported.
>
> That should be, according to the [email protected] archives,
> 3.10.54+, 3.13.11.7+, 3.14.18+, 3.16.2+.
>
Great, thanks for the quick reply. I'll queue the (entire) fix for
the 3.16 kernel.
Cheers,
--
Lu?s
> Paolo
>
> > Cheers,
> > --
> > Lu?s
> >
> >> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> >> index 6e8ce5a1a05d..e0e5642dae41 100644
> >> --- a/arch/x86/kvm/lapic.c
> >> +++ b/arch/x86/kvm/lapic.c
> >> @@ -341,8 +341,12 @@ EXPORT_SYMBOL_GPL(kvm_apic_update_irr);
> >>
> >> static inline void apic_set_irr(int vec, struct kvm_lapic *apic)
> >> {
> >> - apic->irr_pending = true;
> >> apic_set_vector(vec, apic->regs + APIC_IRR);
> >> + /*
> >> + * irr_pending must be true if any interrupt is pending; set it after
> >> + * APIC_IRR to avoid race with apic_clear_irr
> >> + */
> >> + apic->irr_pending = true;
> >> }
> >>
> >> static inline int apic_search_irr(struct kvm_lapic *apic)
> >>
> >>
> >> Thanks,
> >>
> >> Paolo
> >> --
> >> To unsubscribe from this list: send the line "unsubscribe stable" in
> >> the body of a message to [email protected]
> >> More majordomo info at http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe stable" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html