Re: [PATCH 12/13] arm64: Add a capability for FEAT_EVC

[Oliver Upton <oupton@google.com>]

On Mon, Aug 9, 2021 at 9:30 AM Oliver Upton <oupton@google.com> wrote:
>
> Hi Marc,
>
> On Mon, Aug 9, 2021 at 8:48 AM Marc Zyngier <maz@kernel.org> wrote:
> >
> > Add a new capability to detect the Enhanced Counter Virtualization
> > feature (FEAT_EVC).
> >
>
> s/FEAT_EVC/FEAT_ECV/g
>
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  arch/arm64/kernel/cpufeature.c | 10 ++++++++++
> >  arch/arm64/tools/cpucaps       |  1 +
> >  2 files changed, 11 insertions(+)
> >
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index 0ead8bfedf20..9c2ce5408811 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -1899,6 +1899,16 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
> >                 .sign = FTR_UNSIGNED,
> >                 .min_field_value = 1,
> >         },
> > +       {
> > +               .desc = "Enhanced counter virtualization",
> > +               .capability = ARM64_HAS_ECV,
> > +               .type = ARM64_CPUCAP_SYSTEM_FEATURE,
> > +               .matches = has_cpuid_feature,
> > +               .sys_reg = SYS_ID_AA64MMFR0_EL1,
> > +               .field_pos = ID_AA64MMFR0_ECV_SHIFT,
> > +               .sign = FTR_UNSIGNED,
> > +               .min_field_value = 1,
> > +       },
>
> Per one of your other patches in the series, it sounds like userspace
> access to the self-synchronized registers hasn't been settled yet.
> However, if/when available to userspace, should this cpufeature map to
> an ELF HWCAP?
>
> Also, w.r.t. my series I have out for ECV in KVM. All the controls
> used in EL2 depend on ECV=0x2. I agree that ECV=0x1 needs a cpufeature
> bit, but what about EL2's use case?

Forgot to link the series:

http://lore.kernel.org/r/20210804085819.846610-1-oupton@google.com

>
> Besides the typo:
>
> Reviewed-by: Oliver Upton <oupton@google.com>
>
> --
> Thanks,
> Oliver
>
> >  #ifdef CONFIG_ARM64_PAN
> >         {
> >                 .desc = "Privileged Access Never",
> > diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
> > index 49305c2e6dfd..7a7c58acd8f0 100644
> > --- a/arch/arm64/tools/cpucaps
> > +++ b/arch/arm64/tools/cpucaps
> > @@ -18,6 +18,7 @@ HAS_CRC32
> >  HAS_DCPODP
> >  HAS_DCPOP
> >  HAS_E0PD
> > +HAS_ECV
> >  HAS_EPAN
> >  HAS_GENERIC_AUTH
> >  HAS_GENERIC_AUTH_ARCH
> > --
> > 2.30.2
> >