From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Maxim Levitsky <mlevitsk@redhat.com>,
kvm@vger.kernel.org, Vitaly Kuznetsov <vkuznets@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Borislav Petkov <bp@alien8.de>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Joerg Roedel <joro@8bytes.org>, Jim Mattson <jmattson@google.com>
Subject: Re: [PATCH v2 1/4] KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES on nested vmexit
Date: Thu, 7 Jan 2021 11:12:14 -0800 [thread overview]
Message-ID: <X/ddDofjpBVO07/P@google.com> (raw)
In-Reply-To: <6d7bac03-2270-e908-2e66-1cc4f9425294@redhat.com>
On Thu, Jan 07, 2021, Paolo Bonzini wrote:
> On 07/01/21 18:00, Sean Christopherson wrote:
> > Ugh, I assume this is due to one of the "premature" nested_ops->check_events()
> > calls that are necessitated by the event mess? I'm guessing kvm_vcpu_running()
> > is the culprit?
> >
> > If my assumption is correct, this bug affects nVMX as well.
>
> Yes, though it may be latent. For SVM it was until we started allocating
> svm->nested on demand.
>
> > Rather than clear the request blindly on any nested VM-Exit, what
> > about something like the following?
>
> I think your patch is overkill, KVM_REQ_GET_NESTED_STATE_PAGES is only set
> from KVM_SET_NESTED_STATE so it cannot happen while the VM runs.
Yeah, which is why I was hoping we could avoid clearing the request on every
nested exit.
> Something like this is small enough and works well.
I've no argument against it working, rather that I dislike clearing the request
on every exit. Except for the ->check_events() case, hitting the scenario where
there's a pending request at the time of nested VM-Exit would ideally be treated
as a KVM bug.
On the other hand, clearing nested-specific request on nested VM-Exit is
logically sound, so I guess I'm ok with the minimal patch.
next prev parent reply other threads:[~2021-01-07 19:13 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-07 9:38 [PATCH v2 0/4] KVM: nSVM: few random fixes Maxim Levitsky
2021-01-07 9:38 ` [PATCH v2 1/4] KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES on nested vmexit Maxim Levitsky
2021-01-07 17:00 ` Sean Christopherson
2021-01-07 17:51 ` Paolo Bonzini
2021-01-07 17:59 ` Paolo Bonzini
2021-01-07 18:03 ` Maxim Levitsky
2021-01-07 19:12 ` Sean Christopherson [this message]
2021-01-07 9:38 ` [PATCH v2 2/4] KVM: nSVM: correctly restore nested_run_pending on migration Maxim Levitsky
2021-01-07 18:03 ` Paolo Bonzini
2021-01-07 20:19 ` Sean Christopherson
2021-01-07 21:05 ` Paolo Bonzini
2021-01-07 9:38 ` [PATCH v2 3/4] KVM: nSVM: always leave the nested state first on KVM_SET_NESTED_STATE Maxim Levitsky
2021-01-07 9:38 ` [PATCH v2 4/4] KVM: nSVM: mark vmcb as dirty when forcingly leaving the guest mode Maxim Levitsky
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