On Tue, Aug 13, 2024 at 01:47:48PM +0100, Marc Zyngier wrote:
> On Tue, 13 Aug 2024 11:57:10 +0100,
> Joey Gouly <joey.gouly@xxxxxxx> wrote:
> >
> > Hello!
> >
> > On Tue, Aug 13, 2024 at 11:44:00AM +0100, Marc Zyngier wrote:
> > > Everything is now in place for a guest to "enjoy" FP8 support.
> > > Expose ID_AA64PFR2_EL1 to both userspace and guests, with the
> > > explicit restriction of only being able to clear FPMR.
> > >
> > > All other features (MTE* at the time of writing) are hidden
> > > and not writable.
> > >
> > > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> > > ---
> > > arch/arm64/kvm/sys_regs.c | 16 +++++++++++++++-
> > > 1 file changed, 15 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > > index 51627add0a72..da6d017f24a1 100644
> > > --- a/arch/arm64/kvm/sys_regs.c
> > > +++ b/arch/arm64/kvm/sys_regs.c
> > > @@ -1722,6 +1722,15 @@ static u64 read_sanitised_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
> > > return val;
> > > }
> > >
> > > +static u64 read_sanitised_id_aa64pfr2_el1(struct kvm_vcpu *vcpu,
> > > + const struct sys_reg_desc *rd)
> > > +{
> > > + u64 val = read_sanitised_ftr_reg(SYS_ID_AA64PFR2_EL1);
> > > +
> > > + /* We only expose FPMR */
> > > + return val & ID_AA64PFR2_EL1_FPMR;
> > > +}
> >
> > Wondering why you're adding this function instead of extending __kvm_read_sanitised_id_reg()?
> >
> > > +
> > > #define ID_REG_LIMIT_FIELD_ENUM(val, reg, field, limit) \
> > > ({ \
> > > u64 __f_val = FIELD_GET(reg##_##field##_MASK, val); \
> > > @@ -2381,7 +2390,12 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> > > ID_AA64PFR0_EL1_AdvSIMD |
> > > ID_AA64PFR0_EL1_FP), },
> > > ID_SANITISED(ID_AA64PFR1_EL1),
> > > - ID_UNALLOCATED(4,2),
> > > + { SYS_DESC(SYS_ID_AA64PFR2_EL1),
> > > + .access = access_id_reg,
> > > + .get_user = get_id_reg,
> > > + .set_user = set_id_reg,
> > > + .reset = read_sanitised_id_aa64pfr2_el1,
> > > + .val = ID_AA64PFR2_EL1_FPMR, },
> >
> > Then I think this would just be ID_WRITABLE(ID_AA64PFR2_EL1, ID_AA64PFR2_EL1_FPMR).
>
> Yeah, that's an interesting point. I'm afraid I have lost track of the
> many helpers that have been added over time.
>
> Something like this?
LGTM!
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index da6d017f24a1..2d1e45178422 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1539,6 +1539,10 @@ static u64 __kvm_read_sanitised_id_reg(const struct kvm_vcpu *vcpu,
>
> val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_SME);
> break;
> + case SYS_ID_AA64PFR2_EL1:
> + /* We only expose FPMR */
> + val &= ID_AA64PFR2_EL1_FPMR;
> + break;
> case SYS_ID_AA64ISAR1_EL1:
> if (!vcpu_has_ptrauth(vcpu))
> val &= ~(ARM64_FEATURE_MASK(ID_AA64ISAR1_EL1_APA) |
> @@ -1722,15 +1726,6 @@ static u64 read_sanitised_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
> return val;
> }
>
> -static u64 read_sanitised_id_aa64pfr2_el1(struct kvm_vcpu *vcpu,
> - const struct sys_reg_desc *rd)
> -{
> - u64 val = read_sanitised_ftr_reg(SYS_ID_AA64PFR2_EL1);
> -
> - /* We only expose FPMR */
> - return val & ID_AA64PFR2_EL1_FPMR;
> -}
> -
> #define ID_REG_LIMIT_FIELD_ENUM(val, reg, field, limit) \
> ({ \
> u64 __f_val = FIELD_GET(reg##_##field##_MASK, val); \
> @@ -2390,12 +2385,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> ID_AA64PFR0_EL1_AdvSIMD |
> ID_AA64PFR0_EL1_FP), },
> ID_SANITISED(ID_AA64PFR1_EL1),
> - { SYS_DESC(SYS_ID_AA64PFR2_EL1),
> - .access = access_id_reg,
> - .get_user = get_id_reg,
> - .set_user = set_id_reg,
> - .reset = read_sanitised_id_aa64pfr2_el1,
> - .val = ID_AA64PFR2_EL1_FPMR, },
> + ID_WRITABLE(ID_AA64PFR2_EL1, ID_AA64PFR2_EL1_FPMR),
> ID_UNALLOCATED(4,3),
> ID_WRITABLE(ID_AA64ZFR0_EL1, ~ID_AA64ZFR0_EL1_RES0),
> ID_HIDDEN(ID_AA64SMFR0_EL1),
>
> Thanks,
>
> M.
>
> --
> Without deviation from the norm, progress is not possible.
