linux-kernel - Re: [PATCH RFC] KVM: async_pf: fix async

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Message-ID: <579af34a-acea-3aed-ca2c-38fe9fa7da76@redhat.com>
Date:   Thu, 8 Jun 2017 14:48:08 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH RFC] KVM: async_pf: fix async_pf exception injection



On 08/06/2017 14:32, Wanpeng Li wrote:
>>> I change the
>>> condition to "nr == PF_VECTOR && error_code == 0" to intercept async_pf, however,
>>> the below bug will be splatted:
>> Right, because error_code == 0 is a valid error code.
>>
>> For stable releases, this should be enough:
> 
> We should also take care PAGE_READY async_pfs injection. I will send a
> patch to avoid async pf injection stuff in guest mode for stable
> release.

Right, the simplest thing to do here is another is_guest_mode check in
kvm_arch_can_inject_async_page_present.  That would delay the signaling
of ready pages while L2 runs, but hopefully we're under memory pressure
so L2 will get a page fault too.		

In fact, kvm_arch_can_inject_async_page_present should just be

        if (!(vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED))
                return true;
        else
                return can_do_async_pf(vcpu);

where can_do_async_pf becomes nonstatic.
Paolo