Re: [PATCH v7 35/45] arm64: RME: Propagate number of breakpoints and watchpoints to userspace

[Gavin Shan]

On 4/8/25 2:35 AM, Steven Price wrote:
> On 04/03/2025 23:45, Gavin Shan wrote:
> > On 2/14/25 2:14 AM, Steven Price wrote:
> > > From: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > >
> > > The RMM describes the maximum number of BPs/WPs available to the guest
> > > in the Feature Register 0. Propagate those numbers into ID_AA64DFR0_EL1,
> > > which is visible to userspace. A VMM needs this information in order to
> > > set up realm parameters.
> > >
> > > Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > > Signed-off-by: Steven Price <steven.price@xxxxxxx>
> > > ---
> > >    arch/arm64/include/asm/kvm_rme.h |  2 ++
> > >    arch/arm64/kvm/rme.c             | 22 ++++++++++++++++++++++
> > >    arch/arm64/kvm/sys_regs.c        |  2 +-
> > >    3 files changed, 25 insertions(+), 1 deletion(-)
> >
> > With the following one nitpick addressed:
> >
> > Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
> >
> > > diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/
> > > asm/kvm_rme.h
> > > index d684b30493f5..67ee38541a82 100644
> > > --- a/arch/arm64/include/asm/kvm_rme.h
> > > +++ b/arch/arm64/include/asm/kvm_rme.h
> > > @@ -85,6 +85,8 @@ void kvm_init_rme(void);
> > >    u32 kvm_realm_ipa_limit(void);
> > >    u32 kvm_realm_vgic_nr_lr(void);
> > >    +u64 kvm_realm_reset_id_aa64dfr0_el1(const struct kvm_vcpu *vcpu,
> > > u64 val);
> > > +
> > >    bool kvm_rme_supports_sve(void);
> > >      int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap
> > > *cap);
> > > diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
> > > index f83f34358832..8c426f575728 100644
> > > --- a/arch/arm64/kvm/rme.c
> > > +++ b/arch/arm64/kvm/rme.c
> > > @@ -87,6 +87,28 @@ u32 kvm_realm_vgic_nr_lr(void)
> > >        return u64_get_bits(rmm_feat_reg0,
> > > RMI_FEATURE_REGISTER_0_GICV3_NUM_LRS);
> > >    }
> > >    +u64 kvm_realm_reset_id_aa64dfr0_el1(const struct kvm_vcpu *vcpu,
> > > u64 val)
> > > +{
> > > +    u32 bps = u64_get_bits(rmm_feat_reg0,
> > > RMI_FEATURE_REGISTER_0_NUM_BPS);
> > > +    u32 wps = u64_get_bits(rmm_feat_reg0,
> > > RMI_FEATURE_REGISTER_0_NUM_WPS);
> > > +    u32 ctx_cmps;
> > > +
> > > +    if (!kvm_is_realm(vcpu->kvm))
> > > +        return val;
> > > +
> > > +    /* Ensure CTX_CMPs is still valid */
> > > +    ctx_cmps = FIELD_GET(ID_AA64DFR0_EL1_CTX_CMPs, val);
> > > +    ctx_cmps = min(bps, ctx_cmps);
> > > +
> > > +    val &= ~(ID_AA64DFR0_EL1_BRPs_MASK | ID_AA64DFR0_EL1_WRPs_MASK |
> > > +         ID_AA64DFR0_EL1_CTX_CMPs);
> > > +    val |= FIELD_PREP(ID_AA64DFR0_EL1_BRPs_MASK, bps) |
> > > +           FIELD_PREP(ID_AA64DFR0_EL1_WRPs_MASK, wps) |
> > > +           FIELD_PREP(ID_AA64DFR0_EL1_CTX_CMPs, ctx_cmps);
> > > +
> > > +    return val;
> > > +}
> > > +
> >
> > The chunk of code can be squeezed to
> > sys_reg.c::sanitise_id_aa64dfr0_el1() since
> > sys_reg.c has been plumbed for realm, no reason to keep a separate
> > helper in rme.c
> > because it's only called by sys_reg.c::sanitise_id_aa64dfr0_el1()
>
> The issue here is the rmm_feat_reg0 variable - it's currently static in
> rme.c - so I can't just shift the code over. I could obviously provide
> helpers to get the necessary information but this seemed cleaner.

Ack.

Thanks,
Gavin

> Thanks,
> Steve
>
> > >    static int get_start_level(struct realm *realm)
> > >    {
> > >        return 4 - ((realm->ia_bits - 8) / (RMM_PAGE_SHIFT - 3));
> > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > > index ed881725eb64..5618eff33155 100644
> > > --- a/arch/arm64/kvm/sys_regs.c
> > > +++ b/arch/arm64/kvm/sys_regs.c
> > > @@ -1820,7 +1820,7 @@ static u64 sanitise_id_aa64dfr0_el1(const struct
> > > kvm_vcpu *vcpu, u64 val)
> > >        /* Hide BRBE from guests */
> > >        val &= ~ID_AA64DFR0_EL1_BRBE_MASK;
> > >    -    return val;
> > > +    return kvm_realm_reset_id_aa64dfr0_el1(vcpu, val);
> > >    }
> > >      static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,