linux-kernel - Re: [PATCH v9 11/30] KVM: arm64: Define internal features for SME

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Message-ID: <CA+EHjTznZj94NFVQGG8Bi0=kkQUMYA0omdGS++83jwLj-CDRNQ@mail.gmail.com>
Date: Fri, 9 Jan 2026 15:55:36 +0000
From: Fuad Tabba <tabba@...gle.com>
To: Mark Brown <broonie@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>, Joey Gouly <joey.gouly@....com>, 
	Catalin Marinas <catalin.marinas@....com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Will Deacon <will@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>, 
	Shuah Khan <shuah@...nel.org>, Oliver Upton <oupton@...nel.org>, Dave Martin <Dave.Martin@....com>, 
	Mark Rutland <mark.rutland@....com>, Ben Horgan <ben.horgan@....com>, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, Peter Maydell <peter.maydell@...aro.org>, 
	Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH v9 11/30] KVM: arm64: Define internal features for SME

Hi Mark,

On Tue, 23 Dec 2025 at 01:22, Mark Brown <broonie@...nel.org> wrote:
>
> In order to simplify interdependencies in the rest of the series define
> the feature detection for SME and it's subfeatures.  Due to the need for

nit: it's -> its

Reviewed-by: Fuad Tabba <tabba@...gle.com>

Cheers,
/fuad



> vector length configuration we define a flag for SME like for SVE.  We
> also have two subfeatures which add architectural state, FA64 and SME2,
> which are configured via the normal ID register scheme.
>
> Also provide helpers which check if the vCPU is in streaming mode or has
> ZA enabled.
>
> Signed-off-by: Mark Brown <broonie@...nel.org>


> ---
>  arch/arm64/include/asm/kvm_host.h | 35 ++++++++++++++++++++++++++++++++++-
>  arch/arm64/kvm/sys_regs.c         |  2 +-
>  2 files changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 0f3d26467bf0..0816180dc551 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -353,6 +353,8 @@ struct kvm_arch {
>  #define KVM_ARCH_FLAG_WRITABLE_IMP_ID_REGS             10
>         /* Unhandled SEAs are taken to userspace */
>  #define KVM_ARCH_FLAG_EXIT_SEA                         11
> +       /* SME exposed to guest */
> +#define KVM_ARCH_FLAG_GUEST_HAS_SME                    12
>         unsigned long flags;
>
>         /* VM-wide vCPU feature set */
> @@ -1062,7 +1064,16 @@ struct kvm_vcpu_arch {
>  #define vcpu_has_sve(vcpu)     kvm_has_sve((vcpu)->kvm)
>  #endif
>
> -#define vcpu_has_vec(vcpu) vcpu_has_sve(vcpu)
> +#define kvm_has_sme(kvm)       (system_supports_sme() &&               \
> +                                test_bit(KVM_ARCH_FLAG_GUEST_HAS_SME, &(kvm)->arch.flags))
> +
> +#ifdef __KVM_NVHE_HYPERVISOR__
> +#define vcpu_has_sme(vcpu)     kvm_has_sme(kern_hyp_va((vcpu)->kvm))
> +#else
> +#define vcpu_has_sme(vcpu)     kvm_has_sme((vcpu)->kvm)
> +#endif
> +
> +#define vcpu_has_vec(vcpu) (vcpu_has_sve(vcpu) || vcpu_has_sme(vcpu))
>
>  #ifdef CONFIG_ARM64_PTR_AUTH
>  #define vcpu_has_ptrauth(vcpu)                                         \
> @@ -1602,6 +1613,28 @@ void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
>  #define kvm_has_sctlr2(k)                              \
>         (kvm_has_feat((k), ID_AA64MMFR3_EL1, SCTLRX, IMP))
>
> +#define kvm_has_fa64(k)                                        \
> +       (system_supports_fa64() &&                      \
> +        kvm_has_feat((k), ID_AA64SMFR0_EL1, FA64, IMP))
> +
> +#define kvm_has_sme2(k)                                        \
> +       (system_supports_sme2() &&                      \
> +        kvm_has_feat((k), ID_AA64PFR1_EL1, SME, SME2))
> +
> +#ifdef __KVM_NVHE_HYPERVISOR__
> +#define vcpu_has_sme2(vcpu)    kvm_has_sme2(kern_hyp_va((vcpu)->kvm))
> +#define vcpu_has_fa64(vcpu)    kvm_has_fa64(kern_hyp_va((vcpu)->kvm))
> +#else
> +#define vcpu_has_sme2(vcpu)    kvm_has_sme2((vcpu)->kvm)
> +#define vcpu_has_fa64(vcpu)    kvm_has_fa64((vcpu)->kvm)
> +#endif
> +
> +#define vcpu_in_streaming_mode(vcpu) \
> +       (__vcpu_sys_reg(vcpu, SVCR) & SVCR_SM_MASK)
> +
> +#define vcpu_za_enabled(vcpu) \
> +       (__vcpu_sys_reg(vcpu, SVCR) & SVCR_ZA_MASK)
> +
>  static inline bool kvm_arch_has_irq_bypass(void)
>  {
>         return true;
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index c8fd7c6a12a1..3576e69468db 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1945,7 +1945,7 @@ static unsigned int sve_visibility(const struct kvm_vcpu *vcpu,
>  static unsigned int sme_visibility(const struct kvm_vcpu *vcpu,
>                                    const struct sys_reg_desc *rd)
>  {
> -       if (kvm_has_feat(vcpu->kvm, ID_AA64PFR1_EL1, SME, IMP))
> +       if (vcpu_has_sme(vcpu))
>                 return 0;
>
>         return REG_HIDDEN;
>
> --
> 2.47.3
>