From: Gavin Shan <gshan@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>,
x86@kernel.org, kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>
Subject: Re: [PATCH RFC 1/6] Revert "KVM: async_pf: Fix #DF due to inject "Page not Present" and "Page Ready" exceptions simultaneously"
Date: Tue, 5 May 2020 11:22:13 +1000 [thread overview]
Message-ID: <22192687-072e-978b-ac13-fa2fd8d40c59@redhat.com> (raw)
In-Reply-To: <20200429093634.1514902-2-vkuznets@redhat.com>
On 4/29/20 7:36 PM, Vitaly Kuznetsov wrote:
> Commit 9a6e7c39810e (""KVM: async_pf: Fix #DF due to inject "Page not
> Present" and "Page Ready" exceptions simultaneously") added a protection
> against 'page ready' notification coming before 'page not ready' is
> delivered. This situation seems to be impossible since commit 2a266f23550b
> ("KVM MMU: check pending exception before injecting APF) which added
> 'vcpu->arch.exception.pending' check to kvm_can_do_async_pf.
>
> On x86, kvm_arch_async_page_present() has only one call site:
> kvm_check_async_pf_completion() loop and we only enter the loop when
> kvm_arch_can_inject_async_page_present(vcpu) which when async pf msr
> is enabled, translates into kvm_can_do_async_pf().
>
> There is also one problem with the cancellation mechanism. We don't seem
> to check that the 'page not ready' notification we're cancelling matches
> the 'page ready' notification so in theory, we may erroneously drop two
> valid events.
>
> Revert the commit. apf_get_user() stays as we will need it for the new
> 'page ready notifications via interrupt' mechanism.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/x86.c | 16 +---------------
> 1 file changed, 1 insertion(+), 15 deletions(-)
>
Reviewed-by: Gavin Shan <gshan@redhat.com>
next prev parent reply other threads:[~2020-05-05 1:22 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-29 9:36 [PATCH RFC 0/6] KVM: x86: Interrupt-based mechanism for async_pf 'page present' notifications Vitaly Kuznetsov
2020-04-29 9:36 ` [PATCH RFC 1/6] Revert "KVM: async_pf: Fix #DF due to inject "Page not Present" and "Page Ready" exceptions simultaneously" Vitaly Kuznetsov
2020-05-05 1:22 ` Gavin Shan [this message]
2020-05-05 14:16 ` Vivek Goyal
2020-05-06 15:17 ` Vitaly Kuznetsov
2020-05-11 19:17 ` Vivek Goyal
2020-04-29 9:36 ` [PATCH RFC 2/6] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info Vitaly Kuznetsov
2020-05-04 23:52 ` Gavin Shan
2020-05-05 8:08 ` Vitaly Kuznetsov
2020-04-29 9:36 ` [PATCH RFC 3/6] KVM: x86: interrupt based APF page-ready event delivery Vitaly Kuznetsov
2020-04-29 10:54 ` Paolo Bonzini
2020-04-29 12:40 ` Vitaly Kuznetsov
2020-04-29 13:21 ` Paolo Bonzini
2020-04-29 21:27 ` Peter Xu
2020-04-30 8:31 ` Vitaly Kuznetsov
2020-04-30 13:28 ` Peter Xu
2020-04-30 13:49 ` Vitaly Kuznetsov
2020-05-05 15:22 ` Vivek Goyal
2020-04-29 9:36 ` [PATCH RFC 4/6] KVM: x86: acknowledgment mechanism for async pf page ready notifications Vitaly Kuznetsov
2020-04-29 17:28 ` Andy Lutomirski
2020-04-29 17:40 ` Paolo Bonzini
2020-04-30 0:45 ` Andy Lutomirski
2020-04-30 6:46 ` Paolo Bonzini
2020-04-30 6:49 ` Paolo Bonzini
2020-04-30 8:40 ` Vitaly Kuznetsov
2020-04-30 9:27 ` Paolo Bonzini
2020-04-30 11:33 ` Vitaly Kuznetsov
2020-04-30 11:43 ` Paolo Bonzini
2020-05-05 0:36 ` Gavin Shan
2020-05-05 8:16 ` Vitaly Kuznetsov
2020-05-05 8:51 ` Gavin Shan
2020-05-05 9:54 ` Paolo Bonzini
2020-04-29 9:36 ` [PATCH RFC 5/6] KVM: x86: announce KVM_FEATURE_ASYNC_PF_INT Vitaly Kuznetsov
2020-04-29 10:40 ` Peter Zijlstra
2020-04-29 9:36 ` [PATCH RFC 6/6] KVM: x86: Switch KVM guest to using interrupts for page ready APF delivery Vitaly Kuznetsov
2020-04-29 10:53 ` Paolo Bonzini
2020-04-29 12:44 ` Vitaly Kuznetsov
2020-04-29 13:19 ` Paolo Bonzini
2020-04-29 14:34 ` Vitaly Kuznetsov
2020-05-05 18:59 ` Vivek Goyal
2020-05-05 0:42 ` Gavin Shan
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