linux-kernel - Re: [PATCH] x86/cpu: Reinitialize IA32_FEAT

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Date:   Mon, 8 Jun 2020 10:29:21 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Liam Merwick <liam.merwick@...cle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Brad Campbell <lists2009@...rfbargle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH] x86/cpu: Reinitialize IA32_FEAT_CTL MSR on BSP during
 wakeup

On Mon, Jun 08, 2020 at 11:12:35AM +0100, Liam Merwick wrote:
> On 05/06/2020 21:07, Sean Christopherson wrote:
> >Reinitialize IA32_FEAT_CTL on the BSP during wakeup to handle the case
> >where firmware doesn't initialize or save/restore across S3.  This fixes
> >a bug where IA32_FEAT_CTL is left uninitialized and results in VMXON
> >taking a #GP due to VMX not being fully enabled, i.e. breaks KVM.
> >
> >Use init_ia32_feat_ctl() to "restore" IA32_FEAT_CTL as it already deals
> >with the case where the MSR is locked, and because APs already redo
> >init_ia32_feat_ctl() during suspend by virtue of the SMP boot flow being
> >used to reinitialize APs upon wakeup.  Do the call in the early wakeup
> >flow to avoid dependencies in the syscore_ops chain, e.g. simply adding
> >a resume hook is not guaranteed to work, as KVM does VMXON in its own
> >resume hook, kvm_resume(), when KVM has active guests.
> >
> >Reported-by: Brad Campbell <lists2009@...rfbargle.com>
> >Cc: Maxim Levitsky <mlevitsk@...hat.com>
> >Cc: Paolo Bonzini <pbonzini@...hat.com>
> >Cc: kvm@...r.kernel.org
> 
> Should it have the following tag since it fixes a commit introduced in 5.6?
> Cc: stable@...r.kernel.org # v5.6

It definitely warrants a backport to v5.6.  I didn't include a Cc to stable
because I swear I had seen an email fly by that stated an explicit Cc is
unnecessary/unwanted for tip-tree patches, but per a recent statement from
Boris it looks like I'm simply confused[*].  I'll add the Cc in v2.

[*] https://lkml.kernel.org/r/20200417164752.GF7322@zn.tnic

> >Fixes: 21bd3467a58e ("KVM: VMX: Drop initialization of IA32_FEAT_CTL MSR")
> >Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> Reviewed-by: Liam Merwick <liam.merwick@...cle.com>