On Sat, May 28, 2022 at 4:38 AM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> The KVM FP code uses a pair of flags to denote three states:
>
> - FP_ENABLED set: the guest owns the FP state
> - FP_HOST set: the host owns the FP state
> - FP_ENABLED and FP_HOST clear: nobody owns the FP state at all
>
> and both flags set is an illegal state, which nothing ever checks
> for...
>
> As it turns out, this isn't really a good match for flags, and
> we'd be better off if this was a simpler tristate, each state
> having a name that actually reflect the state:
>
> - FP_STATE_CLEAN
> - FP_STATE_HOST_DIRTY
> - FP_STATE_GUEST_DIRTY
>
> Kill the two flags, and move over to an enum encoding these
> three states. This results in less confusing code, and less risk of
> ending up in the uncharted territory of a 4th state if we forget
> to clear one of the two flags.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Reviewed-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
I have the same comment as I have for the patch-3 though.
(i.e. I think having kvm_arch_vcpu_load_fp() set vcpu->arch.fp_state to
FP_STATE_DIRTY_HOST only when FP is supported would be more consistent.)
Thanks,
Reiji
> ---
> arch/arm64/include/asm/kvm_host.h | 9 +++++++--
> arch/arm64/kvm/fpsimd.c | 11 +++++------
> arch/arm64/kvm/hyp/include/hyp/switch.h | 8 +++-----
> arch/arm64/kvm/hyp/nvhe/switch.c | 4 ++--
> arch/arm64/kvm/hyp/vhe/switch.c | 2 +-
> 5 files changed, 18 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 9252d71b4ac5..a46f952b97f6 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -328,6 +328,13 @@ struct kvm_vcpu_arch {
> /* Exception Information */
> struct kvm_vcpu_fault_info fault;
>
> + /* Ownership of the FP regs */
> + enum {
> + FP_STATE_CLEAN,
> + FP_STATE_DIRTY_HOST,
> + FP_STATE_DIRTY_GUEST,
> + } fp_state;
> +
> /* Miscellaneous vcpu state flags */
> u64 flags;
>
> @@ -433,8 +440,6 @@ 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_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 */
> diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
> index 9ebd89541281..0d82f6c5b110 100644
> --- a/arch/arm64/kvm/fpsimd.c
> +++ b/arch/arm64/kvm/fpsimd.c
> @@ -77,8 +77,7 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
> BUG_ON(!current->mm);
> BUG_ON(test_thread_flag(TIF_SVE));
>
> - vcpu->arch.flags &= ~KVM_ARM64_FP_ENABLED;
> - vcpu->arch.flags |= KVM_ARM64_FP_HOST;
> + vcpu->arch.fp_state = FP_STATE_DIRTY_HOST;
>
> vcpu->arch.flags &= ~KVM_ARM64_HOST_SVE_ENABLED;
> if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
> @@ -100,7 +99,7 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
>
> if (read_sysreg_s(SYS_SVCR_EL0) &
> (SYS_SVCR_EL0_SM_MASK | SYS_SVCR_EL0_ZA_MASK)) {
> - vcpu->arch.flags &= ~KVM_ARM64_FP_HOST;
> + vcpu->arch.fp_state = FP_STATE_CLEAN;
> fpsimd_save_and_flush_cpu_state();
> }
> }
> @@ -119,7 +118,7 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
> void kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu *vcpu)
> {
> if (!system_supports_fpsimd() || test_thread_flag(TIF_FOREIGN_FPSTATE))
> - vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED | KVM_ARM64_FP_HOST);
> + vcpu->arch.fp_state = FP_STATE_CLEAN;
> }
>
> /*
> @@ -133,7 +132,7 @@ void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
> {
> WARN_ON_ONCE(!irqs_disabled());
>
> - if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
> + if (vcpu->arch.fp_state == FP_STATE_DIRTY_GUEST) {
> /*
> * Currently we do not support SME guests so SVCR is
> * always 0 and we just need a variable to point to.
> @@ -176,7 +175,7 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
> CPACR_EL1_SMEN_EL1EN);
> }
>
> - if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
> + if (vcpu->arch.fp_state == FP_STATE_DIRTY_GUEST) {
> if (vcpu_has_sve(vcpu)) {
> __vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
>
> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index 1209248d2a3d..b22378abfb57 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -40,7 +40,7 @@ extern struct kvm_exception_table_entry __stop___kvm_ex_table;
> /* Check whether the FP regs are owned by the guest */
> static inline bool guest_owns_fp_regs(struct kvm_vcpu *vcpu)
> {
> - return !!(vcpu->arch.flags & KVM_ARM64_FP_ENABLED);
> + return vcpu->arch.fp_state == FP_STATE_DIRTY_GUEST;
> }
>
> /* Save the 32-bit only FPSIMD system register state */
> @@ -179,10 +179,8 @@ static bool kvm_hyp_handle_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code)
> isb();
>
> /* Write out the host state if it's in the registers */
> - if (vcpu->arch.flags & KVM_ARM64_FP_HOST) {
> + if (vcpu->arch.fp_state == FP_STATE_DIRTY_HOST)
> __fpsimd_save_state(vcpu->arch.host_fpsimd_state);
> - vcpu->arch.flags &= ~KVM_ARM64_FP_HOST;
> - }
>
> /* Restore the guest state */
> if (sve_guest)
> @@ -194,7 +192,7 @@ static bool kvm_hyp_handle_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code)
> if (!(read_sysreg(hcr_el2) & HCR_RW))
> write_sysreg(__vcpu_sys_reg(vcpu, FPEXC32_EL2), fpexc32_el2);
>
> - vcpu->arch.flags |= KVM_ARM64_FP_ENABLED;
> + vcpu->arch.fp_state = FP_STATE_DIRTY_GUEST;
>
> return true;
> }
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index a6b9f1186577..89e0f88c9006 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -123,7 +123,7 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
> }
>
> cptr = CPTR_EL2_DEFAULT;
> - if (vcpu_has_sve(vcpu) && (vcpu->arch.flags & KVM_ARM64_FP_ENABLED))
> + if (vcpu_has_sve(vcpu) && (vcpu->arch.fp_state == FP_STATE_DIRTY_GUEST))
> cptr |= CPTR_EL2_TZ;
> if (cpus_have_final_cap(ARM64_SME))
> cptr &= ~CPTR_EL2_TSM;
> @@ -335,7 +335,7 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
>
> __sysreg_restore_state_nvhe(host_ctxt);
>
> - if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED)
> + if (vcpu->arch.fp_state == FP_STATE_DIRTY_GUEST)
> __fpsimd_save_fpexc32(vcpu);
>
> __debug_switch_to_host(vcpu);
> diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
> index 46f365254e9f..258e87325c95 100644
> --- a/arch/arm64/kvm/hyp/vhe/switch.c
> +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> @@ -175,7 +175,7 @@ static int __kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
>
> sysreg_restore_host_state_vhe(host_ctxt);
>
> - if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED)
> + if (vcpu->arch.fp_state == FP_STATE_DIRTY_GUEST)
> __fpsimd_save_fpexc32(vcpu);
>
> __debug_switch_to_host(vcpu);
> --
> 2.34.1
>
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