Re: [PATCH] x86/cpu: Reinitialize IA32_FEAT_CTL MSR on BSP during wakeup

[Borislav Petkov]

On Mon, Jun 08, 2020 at 10:29:21AM -0700, Sean Christopherson wrote:
> 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@xxxxxxxxxxxxxxx>
> > >Cc: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> > >Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > >Cc: kvm@xxxxxxxxxxxxxxx
> > 
> > Should it have the following tag since it fixes a commit introduced in 5.6?
> > Cc: stable@xxxxxxxxxxxxxxx # 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@xxxxxxx

Yeah, I was simply parroting what Greg has told me. Maybe he should
finally do that script. :-P

Also, I believe Sasha's Skynet machine already does that...

CCed both.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette