Subject: Re: [PATCH v2] arm64: Unify WORKAROUND_SPECULATIVE_AT_{NVHE,VHE}

From: Andrew Scull <[email-masked]>
Date: Thu, 30 Apr 2020 10:26:58 +0100

On Thu, Apr 30, 2020 at 10:16:03AM +0100, Marc Zyngier wrote:
> On 2020-04-29 22:21, Will Deacon wrote:
> > Hi Andrew,
> > 
> > On Wed, Apr 22, 2020 at 05:13:46PM +0100, Andrew Scull wrote:
> > > Errata 1165522, 1319367 and 1530923 each allow TLB entries to be
> > > allocated as a result of a speculative AT instruction. In order to
> > > avoid mandating VHE on certain affected CPUs, apply the workaround to
> > > both the nVHE and the VHE case for all affected CPUs.
> > > 
> > > Signed-off-by: Andrew Scull <[email-masked]>
> > > CC: Marc Zyngier <[email-masked]>
> > > CC: James Morse <[email-masked]>
> > > CC: Suzuki K Poulose <[email-masked]>
> > > CC: Will Deacon <[email-masked]>
> > > CC: Steven Price <[email-masked]>
> > > ---
> > > * From v1 <[email-masked]>:
> > >   - Restored registers in VHE path
> > 
> > This largely looks good to me, but I don't understand these bits:
> > 
> > > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> > > index 8a1e81a400e0..651820f537fb 100644
> > > --- a/arch/arm64/kvm/hyp/switch.c
> > > +++ b/arch/arm64/kvm/hyp/switch.c
> > > @@ -138,7 +138,7 @@ static void __hyp_text
> > > __activate_traps_nvhe(struct kvm_vcpu *vcpu)
> > > 
> > >  	write_sysreg(val, cptr_el2);
> > > 
> > > -	if (cpus_have_final_cap(ARM64_WORKAROUND_SPECULATIVE_AT_NVHE)) {
> > > +	if (cpus_have_const_cap(ARM64_WORKAROUND_SPECULATIVE_AT)) {
> > 
> > It seems like you consistently replace cpus_have_final_cap() with
> > cpus_have_const_cap(), but I can't figure out why that's required.
> 
> Seems like a bad conflict resolution. We definitely want to keep the
> final_cap checks for anything that will run at EL2, and probably
> everywhere else (if capabilities are not final by the time we hit KVM,
> we have bigger problems to solve).
> 
> Thanks,
> 
>         M.
> -- 
> Jazz is not dead. It just smells funny...

Indeed, those weren't the 5 characters my eye was interested in. Looks
like we'll be having a v3..

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