KVM: arm64: Add save/restore support for FPMR

Just like the rest of the FP/SIMD state, FPMR needs to be context
switched.

The only interesting thing here is that we need to treat the pKVM
part a bit differently, as the host FP state is never written back
to the vcpu thread, but instead stored locally and eagerly restored.

Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240820131802.3547589-5-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Marc Zyngier

arch/arm64/include/asm/kvm_host.h

@@ -599,6 +599,16 @@ struct kvm_host_data {
 		struct cpu_sve_state *sve_state;
 	};
 
+	union {
+		/* HYP VA pointer to the host storage for FPMR */
+		u64	*fpmr_ptr;
+		/*
+		 * Used by pKVM only, as it needs to provide storage
+		 * for the host
+		 */
+		u64	fpmr;
+	};
+
 	/* Ownership of the FP regs */
 	enum {
 		FP_STATE_FREE,

arch/arm64/kvm/fpsimd.c

@@ -63,6 +63,7 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
 	 */
 	*host_data_ptr(fp_owner) = FP_STATE_HOST_OWNED;
 	*host_data_ptr(fpsimd_state) = kern_hyp_va(&current->thread.uw.fpsimd_state);
+	*host_data_ptr(fpmr_ptr) = kern_hyp_va(&current->thread.uw.fpmr);
 
 	vcpu_clear_flag(vcpu, HOST_SVE_ENABLED);
 	if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)

arch/arm64/kvm/hyp/include/hyp/switch.h

@@ -404,6 +404,9 @@ static bool kvm_hyp_handle_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code)
 	else
 		__fpsimd_restore_state(&vcpu->arch.ctxt.fp_regs);
 
+	if (kvm_has_fpmr(kern_hyp_va(vcpu->kvm)))
+		write_sysreg_s(__vcpu_sys_reg(vcpu, FPMR), SYS_FPMR);
+
 	/* Skip restoring fpexc32 for AArch64 guests */
 	if (!(read_sysreg(hcr_el2) & HCR_RW))
 		write_sysreg(__vcpu_sys_reg(vcpu, FPEXC32_EL2), fpexc32_el2);

arch/arm64/kvm/hyp/nvhe/hyp-main.c

@@ -62,6 +62,8 @@ static void fpsimd_sve_flush(void)
 
 static void fpsimd_sve_sync(struct kvm_vcpu *vcpu)
 {
+	bool has_fpmr;
+
 	if (!guest_owns_fp_regs())
 		return;
 
@@ -73,11 +75,18 @@ static void fpsimd_sve_sync(struct kvm_vcpu *vcpu)
 	else
 		__fpsimd_save_state(&vcpu->arch.ctxt.fp_regs);
 
+	has_fpmr = kvm_has_fpmr(kern_hyp_va(vcpu->kvm));
+	if (has_fpmr)
+		__vcpu_sys_reg(vcpu, FPMR) = read_sysreg_s(SYS_FPMR);
+
 	if (system_supports_sve())
 		__hyp_sve_restore_host();
 	else
 		__fpsimd_restore_state(*host_data_ptr(fpsimd_state));
 
+	if (has_fpmr)
+		write_sysreg_s(*host_data_ptr(fpmr), SYS_FPMR);
+
 	*host_data_ptr(fp_owner) = FP_STATE_HOST_OWNED;
 }
 

arch/arm64/kvm/hyp/nvhe/switch.c

@@ -198,6 +198,15 @@ static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu)
 	} else {
 		__fpsimd_save_state(*host_data_ptr(fpsimd_state));
 	}
+
+	if (kvm_has_fpmr(kern_hyp_va(vcpu->kvm))) {
+		u64 val = read_sysreg_s(SYS_FPMR);
+
+		if (unlikely(is_protected_kvm_enabled()))
+			*host_data_ptr(fpmr) = val;
+		else
+			**host_data_ptr(fpmr_ptr) = val;
+	}
 }
 
 static const exit_handler_fn hyp_exit_handlers[] = {

arch/arm64/kvm/hyp/vhe/switch.c

@@ -312,6 +312,9 @@ static bool kvm_hyp_handle_eret(struct kvm_vcpu *vcpu, u64 *exit_code)
 static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu)
 {
 	__fpsimd_save_state(*host_data_ptr(fpsimd_state));
+
+	if (kvm_has_fpmr(vcpu->kvm))
+		**host_data_ptr(fpmr_ptr) = read_sysreg_s(SYS_FPMR);
 }
 
 static bool kvm_hyp_handle_tlbi_el2(struct kvm_vcpu *vcpu, u64 *exit_code)