On Tue, 23 Dec 2025 at 01:22, Mark Brown <broonie@kernel.org> wrote:
>
> SME is configured by the system registers SMCR_EL1 and SMCR_EL2, add
> definitions and userspace access for them. These control the SME vector
> length in a manner similar to that for SVE and also have feature enable
> bits for SME2 and FA64. A subsequent patch will add management of them
> for guests as part of the general floating point context switch, as is
> done for the equivalent SVE registers.
>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
> arch/arm64/include/asm/kvm_host.h | 2 ++
> arch/arm64/include/asm/vncr_mapping.h | 1 +
> arch/arm64/kvm/sys_regs.c | 36 ++++++++++++++++++++++++++++++++++-
> 3 files changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index b41700df3ce9..f24441244a68 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -504,6 +504,7 @@ enum vcpu_sysreg {
> CPTR_EL2, /* Architectural Feature Trap Register (EL2) */
> HACR_EL2, /* Hypervisor Auxiliary Control Register */
> ZCR_EL2, /* SVE Control Register (EL2) */
> + SMCR_EL2, /* SME Control Register (EL2) */
> TTBR0_EL2, /* Translation Table Base Register 0 (EL2) */
> TTBR1_EL2, /* Translation Table Base Register 1 (EL2) */
> TCR_EL2, /* Translation Control Register (EL2) */
> @@ -542,6 +543,7 @@ enum vcpu_sysreg {
> VNCR(ACTLR_EL1),/* Auxiliary Control Register */
> VNCR(CPACR_EL1),/* Coprocessor Access Control */
> VNCR(ZCR_EL1), /* SVE Control */
> + VNCR(SMCR_EL1), /* SME Control */
> VNCR(TTBR0_EL1),/* Translation Table Base Register 0 */
> VNCR(TTBR1_EL1),/* Translation Table Base Register 1 */
> VNCR(TCR_EL1), /* Translation Control Register */
> diff --git a/arch/arm64/include/asm/vncr_mapping.h b/arch/arm64/include/asm/vncr_mapping.h
> index c2485a862e69..44b12565321b 100644
> --- a/arch/arm64/include/asm/vncr_mapping.h
> +++ b/arch/arm64/include/asm/vncr_mapping.h
> @@ -44,6 +44,7 @@
> #define VNCR_HDFGWTR_EL2 0x1D8
> #define VNCR_ZCR_EL1 0x1E0
> #define VNCR_HAFGRTR_EL2 0x1E8
> +#define VNCR_SMCR_EL1 0x1F0
> #define VNCR_TTBR0_EL1 0x200
> #define VNCR_TTBR1_EL1 0x210
> #define VNCR_FAR_EL1 0x220
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 3576e69468db..5c912139d264 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -2827,6 +2827,37 @@ static bool access_gic_elrsr(struct kvm_vcpu *vcpu,
> return true;
> }
>
> +static unsigned int sme_el2_visibility(const struct kvm_vcpu *vcpu,
> + const struct sys_reg_desc *rd)
> +{
> + return __el2_visibility(vcpu, rd, sme_visibility);
> +}
> +
> +static bool access_smcr_el2(struct kvm_vcpu *vcpu,
> + struct sys_reg_params *p,
> + const struct sys_reg_desc *r)
> +{
> + unsigned int vq;
> + u64 smcr;
> +
> + if (guest_hyp_sve_traps_enabled(vcpu)) {
Should this be guest_hyp_sme_traps_enabled() ?
> + kvm_inject_nested_sve_trap(vcpu);
And by the same token, should this be kvm_inject_nested_sme_trap()?
That function doesn't exist, but would inject ESR_ELx_EC_SME instead
of ESR_ELx_EC_SVE.
> + return false;
> + }
> +
> + if (!p->is_write) {
> + p->regval = __vcpu_sys_reg(vcpu, SMCR_EL2);
> + return true;
> + }
> +
> + smcr = p->regval;
> + vq = SYS_FIELD_GET(SMCR_ELx, LEN, smcr) + 1;
> + vq = min(vq, vcpu_sme_max_vq(vcpu));
> + __vcpu_assign_sys_reg(vcpu, SMCR_EL2, SYS_FIELD_PREP(SMCR_ELx, LEN,
> + vq - 1));
I think this might be wrong. This code only writes the LEN, discarding
other fields in SMCR_EL2. The analogous SVE code in access_zcr_el2()
is only concerned with the length, and doesn't need to worry about
other bits to preserve.
Should this be something along the lines of the below instead?
+ smcr = p->regval;
+ vq = SYS_FIELD_GET(SMCR_ELx, LEN, smcr) + 1;
+ vq = min(vq, vcpu_sme_max_vq(vcpu));
+ smcr &= ~SMCR_ELx_LEN_MASK;
+ smcr |= SYS_FIELD_PREP(SMCR_ELx, LEN, vq - 1);
+ __vcpu_assign_sys_reg(vcpu, SMCR_EL2, smcr);
Cheers,
/fuad
> + return true;
> +}
> +
> static unsigned int s1poe_visibility(const struct kvm_vcpu *vcpu,
> const struct sys_reg_desc *rd)
> {
> @@ -3291,7 +3322,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> { SYS_DESC(SYS_ZCR_EL1), NULL, reset_val, ZCR_EL1, 0, .visibility = sve_visibility },
> { SYS_DESC(SYS_TRFCR_EL1), undef_access },
> { SYS_DESC(SYS_SMPRI_EL1), undef_access },
> - { SYS_DESC(SYS_SMCR_EL1), undef_access },
> + { SYS_DESC(SYS_SMCR_EL1), NULL, reset_val, SMCR_EL1, 0, .visibility = sme_visibility },
> { SYS_DESC(SYS_TTBR0_EL1), access_vm_reg, reset_unknown, TTBR0_EL1 },
> { SYS_DESC(SYS_TTBR1_EL1), access_vm_reg, reset_unknown, TTBR1_EL1 },
> { SYS_DESC(SYS_TCR_EL1), access_vm_reg, reset_val, TCR_EL1, 0 },
> @@ -3655,6 +3686,9 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>
> EL2_REG_VNCR(HCRX_EL2, reset_val, 0),
>
> + EL2_REG_FILTERED(SMCR_EL2, access_smcr_el2, reset_val, 0,
> + sme_el2_visibility),
> +
> EL2_REG(TTBR0_EL2, access_rw, reset_val, 0),
> EL2_REG(TTBR1_EL2, access_rw, reset_val, 0),
> EL2_REG(TCR_EL2, access_rw, reset_val, TCR_EL2_RES1),
>
> --
> 2.47.3
>