KVM: arm64: Move FP state ownership from flag to a tristate

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_FREE
- FP_STATE_HOST_OWNED
- FP_STATE_GUEST_OWNED

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@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Reiji Watanabe <reijiw@google.com>

1 files changed, 6 insertions, 8 deletions

diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index edbc0183c89b..d397efe1a378 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_HOST_OWNED;
 
 	vcpu->arch.flags &= ~KVM_ARM64_HOST_SVE_ENABLED;
 	if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
@@ -98,9 +97,8 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
 		if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
 			vcpu->arch.flags |= KVM_ARM64_HOST_SME_ENABLED;
 
-		if (read_sysreg_s(SYS_SVCR) &
-		    (SVCR_SM_MASK | SVCR_ZA_MASK)) {
-			vcpu->arch.flags &= ~KVM_ARM64_FP_HOST;
+		if (read_sysreg_s(SYS_SVCR) & (SVCR_SM_MASK | SVCR_ZA_MASK)) {
+			vcpu->arch.fp_state = FP_STATE_FREE;
 			fpsimd_save_and_flush_cpu_state();
 		}
 	}
@@ -119,7 +117,7 @@ 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_FREE;
 }
 
 /*
@@ -133,7 +131,7 @@ 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_GUEST_OWNED) {
 		/*
 		 * Currently we do not support SME guests so SVCR is
 		 * always 0 and we just need a variable to point to.
@@ -176,7 +174,7 @@ 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_GUEST_OWNED) {
 		if (vcpu_has_sve(vcpu)) {
 			__vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);