Some parts of the SME state are optional, enabled by additional features on top of the base FEAT_SME and controlled with enable bits in SMCR_ELx. We unconditionally enable these for the host but for KVM we will allow the feature set exposed to guests to be restricted by the VMM. These are the FFR register (FEAT_SME_FA64) and ZT0 (FEAT_SME2).
We defer saving of guest floating point state for non-protected guests to the host kernel. We also want to avoid having to reconfigure the guest floating point state if nothing used the floating point state while running the host. If the guest was running with the optional features disabled then traps will be enabled for them so the host kernel will need to skip accessing that state when saving state for the guest.
Support this by moving the decision about saving this state to the point where we bind floating point state to the CPU, adding a new variable to the cpu_fp_state which uses the enable bits in SMCR_ELx to flag which features are enabled.
Signed-off-by: Mark Brown broonie@kernel.org --- arch/arm64/include/asm/fpsimd.h | 1 + arch/arm64/kernel/fpsimd.c | 10 ++++++++-- arch/arm64/kvm/fpsimd.c | 1 + 3 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h index ece65061dea0..146c1af55e22 100644 --- a/arch/arm64/include/asm/fpsimd.h +++ b/arch/arm64/include/asm/fpsimd.h @@ -87,6 +87,7 @@ struct cpu_fp_state { void *sme_state; u64 *svcr; u64 *fpmr; + u64 sme_features; unsigned int sve_vl; unsigned int sme_vl; enum fp_type *fp_type; diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index be4499ff6498..887fce177c92 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -490,12 +490,12 @@ static void fpsimd_save_user_state(void)
if (*svcr & SVCR_ZA_MASK) sme_save_state(last->sme_state, - system_supports_sme2()); + last->sme_features & SMCR_ELx_EZT0);
/* If we are in streaming mode override regular SVE. */ if (*svcr & SVCR_SM_MASK) { save_sve_regs = true; - save_ffr = system_supports_fa64(); + save_ffr = last->sme_features & SMCR_ELx_FA64; vl = last->sme_vl; } } @@ -1671,6 +1671,12 @@ static void fpsimd_bind_task_to_cpu(void) last->to_save = FP_STATE_CURRENT; current->thread.fpsimd_cpu = smp_processor_id();
+ last->sme_features = 0; + if (system_supports_fa64()) + last->sme_features |= SMCR_ELx_FA64; + if (system_supports_sme2()) + last->sme_features |= SMCR_ELx_EZT0; + /* * Toggle SVE and SME trapping for userspace if needed, these * are serialsied by ret_to_user(). diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c index 15e17aca1dec..9158353d8be3 100644 --- a/arch/arm64/kvm/fpsimd.c +++ b/arch/arm64/kvm/fpsimd.c @@ -80,6 +80,7 @@ void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu) fp_state.svcr = __ctxt_sys_reg(&vcpu->arch.ctxt, SVCR); fp_state.fpmr = __ctxt_sys_reg(&vcpu->arch.ctxt, FPMR); fp_state.fp_type = &vcpu->arch.fp_type; + fp_state.sme_features = 0;
if (vcpu_has_sve(vcpu)) fp_state.to_save = FP_STATE_SVE;