On Tue, Jul 07, 2020 at 03:57:13PM +0100, Andrew Scull wrote: > The FPSIMD registers can be in one of three states: > (a) loaded with the user task's state > (b) loaded with the vcpu's state > (c) dirty with transient state > > KVM_ARM64_FP_HOST identifies the case (a). When loading the vcpu state, > this is used to decide whether to save the current FPSIMD registers to > the user task. > > However, at the point of loading the vcpu's FPSIMD state, it is known > that we are not in state (b). States (a) and (c) can be distinguished by > by checking the TIF_FOREIGN_FPSTATE bit, as was previously being done to > prepare the KVM_ARM64_FP_HOST flag but without the need for mirroring > the state. > > Signed-off-by: Andrew Scull <ascull@xxxxxxxxxx> Is your new series [1] intended to replace this, or do I need to look at both series now? Cheers ---Dave [1] Manage vcpu flags from the host https://lists.cs.columbia.edu/pipermail/kvmarm/2020-July/041531.html > --- > This is the result of trying to get my head around the FPSIMD handling. > If I've misunderstood something I'll be very happy to have it explained > to me :) > --- > arch/arm64/include/asm/kvm_host.h | 11 +++++---- > arch/arm64/kvm/fpsimd.c | 1 - > arch/arm64/kvm/hyp/include/hyp/switch.h | 30 +++++++++++++++++-------- > 3 files changed, 26 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index e0920df1d0c1..d3652745282d 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -370,12 +370,11 @@ struct kvm_vcpu_arch { > /* vcpu_arch flags field values: */ > #define KVM_ARM64_DEBUG_DIRTY (1 << 0) > #define KVM_ARM64_FP_ENABLED (1 << 1) /* guest FP regs loaded */ > -#define KVM_ARM64_FP_HOST (1 << 2) /* host FP regs loaded */ > -#define KVM_ARM64_HOST_SVE_IN_USE (1 << 3) /* backup for host TIF_SVE */ > -#define KVM_ARM64_HOST_SVE_ENABLED (1 << 4) /* SVE enabled for EL0 */ > -#define KVM_ARM64_GUEST_HAS_SVE (1 << 5) /* SVE exposed to guest */ > -#define KVM_ARM64_VCPU_SVE_FINALIZED (1 << 6) /* SVE config completed */ > -#define KVM_ARM64_GUEST_HAS_PTRAUTH (1 << 7) /* PTRAUTH exposed to guest */ > +#define KVM_ARM64_HOST_SVE_IN_USE (1 << 2) /* backup for host TIF_SVE */ > +#define KVM_ARM64_HOST_SVE_ENABLED (1 << 3) /* SVE enabled for EL0 */ > +#define KVM_ARM64_GUEST_HAS_SVE (1 << 4) /* SVE exposed to guest */ > +#define KVM_ARM64_VCPU_SVE_FINALIZED (1 << 5) /* SVE config completed */ > +#define KVM_ARM64_GUEST_HAS_PTRAUTH (1 << 6) /* PTRAUTH exposed to guest */ > > #define vcpu_has_sve(vcpu) (system_supports_sve() && \ > ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE)) > diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c > index e329a36b2bee..4e9afeb31989 100644 > --- a/arch/arm64/kvm/fpsimd.c > +++ b/arch/arm64/kvm/fpsimd.c > @@ -65,7 +65,6 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) > vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED | > KVM_ARM64_HOST_SVE_IN_USE | > KVM_ARM64_HOST_SVE_ENABLED); > - vcpu->arch.flags |= KVM_ARM64_FP_HOST; > > if (test_thread_flag(TIF_SVE)) > vcpu->arch.flags |= KVM_ARM64_HOST_SVE_IN_USE; > diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h > index 8f622688fa64..beadf17f12a6 100644 > --- a/arch/arm64/kvm/hyp/include/hyp/switch.h > +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h > @@ -33,16 +33,24 @@ extern const char __hyp_panic_string[]; > static inline bool update_fp_enabled(struct kvm_vcpu *vcpu) > { > /* > - * When the system doesn't support FP/SIMD, we cannot rely on > - * the _TIF_FOREIGN_FPSTATE flag. However, we always inject an > - * abort on the very first access to FP and thus we should never > - * see KVM_ARM64_FP_ENABLED. For added safety, make sure we always > + * When entering the vcpu during a KVM_VCPU_RUN call before the vcpu > + * has used FPSIMD, FPSIMD is disabled for the vcpu and will trap when > + * it is first used. The FPSIMD state currently bound to the cpu is > + * that of the user task. > + * > + * After the vcpu has used FPSIMD, on subsequent entries into the vcpu > + * for the same KVM_VCPU_RUN call, the vcpu's FPSIMD state is bound to > + * the cpu. Therefore, if _TIF_FOREIGN_FPSTATE is set, we know the > + * FPSIMD registers no longer contain the vcpu's state. In this case we > + * must, once again, disable FPSIMD. > + * > + * When the system doesn't support FPSIMD, we cannot rely on the > + * _TIF_FOREIGN_FPSTATE flag. For added safety, make sure we always > * trap the accesses. > */ > if (!system_supports_fpsimd() || > vcpu->arch.host_thread_info->flags & _TIF_FOREIGN_FPSTATE) > - vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED | > - KVM_ARM64_FP_HOST); > + vcpu->arch.flags &= ~KVM_ARM64_FP_ENABLED; > > return !!(vcpu->arch.flags & KVM_ARM64_FP_ENABLED); > } > @@ -245,7 +253,13 @@ static inline bool __hyp_handle_fpsimd(struct kvm_vcpu *vcpu) > > isb(); > > - if (vcpu->arch.flags & KVM_ARM64_FP_HOST) { > + /* > + * The trap means that the vcpu's FPSIMD state is not loaded. If > + * _TIF_FOREIGN_FPSTATE is set, the current state does not need to be > + * saved. Otherwise, the user task's state is currently loaded and > + * needs to be saved. > + */ > + if (!(vcpu->arch.host_thread_info->flags & _TIF_FOREIGN_FPSTATE)) { > /* > * In the SVE case, VHE is assumed: it is enforced by > * Kconfig and kvm_arch_init(). > @@ -260,8 +274,6 @@ static inline bool __hyp_handle_fpsimd(struct kvm_vcpu *vcpu) > } else { > __fpsimd_save_state(vcpu->arch.host_fpsimd_state); > } > - > - vcpu->arch.flags &= ~KVM_ARM64_FP_HOST; > } > > if (sve_guest) { > -- > 2.27.0.383.g050319c2ae-goog > > _______________________________________________ > kvmarm mailing list > kvmarm@xxxxxxxxxxxxxxxxxxxxx > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
