[PATCH] KVM MMU: check pending exception before injecting APF

[PATCH] KVM MMU: check pending exception before injecting APF

[Paolo Bonzini]

From: Haozhong Zhang <haozhong.zhang@intel.com>

[ upstream commit 2a266f23550be997d783f27e704b9b40c4010292 Mon Sep 17 00:00:00 2001 ]

For example, when two APF's for page ready happen after one exit and
the first one becomes pending, the second one will result in #DF.
Instead, just handle the second page fault synchronously.

Reported-by: Ross Zwisler <zwisler@gmail.com>
Message-ID: <CAOxpaSUBf8QoOZQ1p4KfUp0jq76OKfGY4Uxs-Gg8ngReD99xww@mail.gmail.com>
Reported-by: Alec Blayne <ab@tevsa.net>
Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
Fixes: 664f8e26b00c7673a8303b0d40853a0c24ca93e1
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c4deb1f34faa..e577bacd4bd0 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3781,7 +3781,8 @@ static int kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn)
 bool kvm_can_do_async_pf(struct kvm_vcpu *vcpu)
 {
 	if (unlikely(!lapic_in_kernel(vcpu) ||
-		     kvm_event_needs_reinjection(vcpu)))
+		     kvm_event_needs_reinjection(vcpu) ||
+		     vcpu->arch.exception.pending))
 		return false;
 
 	if (!vcpu->arch.apf.delivery_as_pf_vmexit && is_guest_mode(vcpu))
-- 
1.8.3.1

Re: [PATCH] KVM MMU: check pending exception before injecting APF

[Greg KH]

On Fri, Feb 09, 2018 at 06:00:42PM +0100, Paolo Bonzini wrote:
> From: Haozhong Zhang <haozhong.zhang@intel.com>
> 
> [ upstream commit 2a266f23550be997d783f27e704b9b40c4010292 Mon Sep 17 00:00:00 2001 ]

Odd date :)

> 
> For example, when two APF's for page ready happen after one exit and
> the first one becomes pending, the second one will result in #DF.
> Instead, just handle the second page fault synchronously.
> 
> Reported-by: Ross Zwisler <zwisler@gmail.com>
> Message-ID: <CAOxpaSUBf8QoOZQ1p4KfUp0jq76OKfGY4Uxs-Gg8ngReD99xww@mail.gmail.com>
> Reported-by: Alec Blayne <ab@tevsa.net>
> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> Fixes: 664f8e26b00c7673a8303b0d40853a0c24ca93e1

So this is only needed for 4.14.y?

thanks,

greg k-h

Re: [PATCH] KVM MMU: check pending exception before injecting APF

[Paolo Bonzini]

On 09/02/2018 18:17, Greg KH wrote:
> On Fri, Feb 09, 2018 at 06:00:42PM +0100, Paolo Bonzini wrote:
>> From: Haozhong Zhang <haozhong.zhang@intel.com>
>>
>> [ upstream commit 2a266f23550be997d783f27e704b9b40c4010292 Mon Sep 17 00:00:00 2001 ]
> 
> Odd date :)

Oops... git's fake mbox "From" line.

>>
>> For example, when two APF's for page ready happen after one exit and
>> the first one becomes pending, the second one will result in #DF.
>> Instead, just handle the second page fault synchronously.
>>
>> Reported-by: Ross Zwisler <zwisler@gmail.com>
>> Message-ID: <CAOxpaSUBf8QoOZQ1p4KfUp0jq76OKfGY4Uxs-Gg8ngReD99xww@mail.gmail.com>
>> Reported-by: Alec Blayne <ab@tevsa.net>
>> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
>> Fixes: 664f8e26b00c7673a8303b0d40853a0c24ca93e1
> 
> So this is only needed for 4.14.y?

Yes.  4.13 and 4.15 both work.

Paolo

Re: [PATCH] KVM MMU: check pending exception before injecting APF

[Greg KH]

On Fri, Feb 09, 2018 at 06:21:13PM +0100, Paolo Bonzini wrote:
> On 09/02/2018 18:17, Greg KH wrote:
> > On Fri, Feb 09, 2018 at 06:00:42PM +0100, Paolo Bonzini wrote:
> >> From: Haozhong Zhang <haozhong.zhang@intel.com>
> >>
> >> [ upstream commit 2a266f23550be997d783f27e704b9b40c4010292 Mon Sep 17 00:00:00 2001 ]
> > 
> > Odd date :)
> 
> Oops... git's fake mbox "From" line.

Yeah, I guessed, odd it showed up here...

> >> For example, when two APF's for page ready happen after one exit and
> >> the first one becomes pending, the second one will result in #DF.
> >> Instead, just handle the second page fault synchronously.
> >>
> >> Reported-by: Ross Zwisler <zwisler@gmail.com>
> >> Message-ID: <CAOxpaSUBf8QoOZQ1p4KfUp0jq76OKfGY4Uxs-Gg8ngReD99xww@mail.gmail.com>
> >> Reported-by: Alec Blayne <ab@tevsa.net>
> >> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> >> Fixes: 664f8e26b00c7673a8303b0d40853a0c24ca93e1
> > 
> > So this is only needed for 4.14.y?
> 
> Yes.  4.13 and 4.15 both work.

Wonderful, I'll queue this up after this round of kernels are released
in a few days.

thanks,

greg k-h