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, 3 insertions, 5 deletions

diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index e54320384943..6cbbb6c02f66 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_GUEST_OWNED;
 }
 
 /* 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_HOST_OWNED)
 		__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_GUEST_OWNED;
 
 	return true;
 }