KVM: arm64: Remove host FPSIMD saving for non-protected KVM

Now that the host eagerly saves its own FPSIMD/SVE/SME state,
non-protected KVM never needs to save the host FPSIMD/SVE/SME state,
and the code to do this is never used. Protected KVM still needs to
save/restore the host FPSIMD/SVE state to avoid leaking guest state to
the host (and to avoid revealing to the host whether the guest used
FPSIMD/SVE/SME), and that code needs to be retained.

Remove the unused code and data structures.

To avoid the need for a stub copy of kvm_hyp_save_fpsimd_host() in the
VHE hyp code, the nVHE/hVHE version is moved into the shared switch
header, where it is only invoked when KVM is in protected mode.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-3-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_host.h

@@ -624,23 +624,13 @@ struct kvm_host_data {
 	struct kvm_cpu_context host_ctxt;
 
 	/*
-	 * All pointers in this union are hyp VA.
+	 * Hyp VA.
 	 * sve_state is only used in pKVM and if system_supports_sve().
 	 */
-	union {
+	struct cpu_sve_state *sve_state;
-		struct user_fpsimd_state *fpsimd_state;
-		struct cpu_sve_state *sve_state;
-	};
 
-	union {
+	/* Used by pKVM only. */
-		/* HYP VA pointer to the host storage for FPMR */
+	u64	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 {

arch/arm64/kvm/arm.c

@@ -2481,14 +2481,6 @@ static void finalize_init_hyp_mode(void)
 			per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->sve_state =
 				kern_hyp_va(sve_state);
 		}
-	} else {
-		for_each_possible_cpu(cpu) {
-			struct user_fpsimd_state *fpsimd_state;
-
-			fpsimd_state = &per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->host_ctxt.fp_regs;
-			per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->fpsimd_state =
-				kern_hyp_va(fpsimd_state);
-		}
 	}
 }
 

arch/arm64/kvm/fpsimd.c

@@ -64,8 +64,6 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
 	 */
 	fpsimd_save_and_flush_cpu_state();
 	*host_data_ptr(fp_owner) = FP_STATE_FREE;
-	*host_data_ptr(fpsimd_state) = NULL;
-	*host_data_ptr(fpmr_ptr) = NULL;
 
 	host_data_clear_flag(HOST_SVE_ENABLED);
 	if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)

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

@@ -375,7 +375,28 @@ static inline void __hyp_sve_save_host(void)
 			 true);
 }
 
-static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu);
+static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * Non-protected kvm relies on the host restoring its sve state.
+	 * Protected kvm restores the host's sve state as not to reveal that
+	 * fpsimd was used by a guest nor leak upper sve bits.
+	 */
+	if (system_supports_sve()) {
+		__hyp_sve_save_host();
+
+		/* Re-enable SVE traps if not supported for the guest vcpu. */
+		if (!vcpu_has_sve(vcpu))
+			cpacr_clear_set(CPACR_EL1_ZEN, 0);
+
+	} else {
+		__fpsimd_save_state(host_data_ptr(host_ctxt.fp_regs));
+	}
+
+	if (kvm_has_fpmr(kern_hyp_va(vcpu->kvm)))
+		*host_data_ptr(fpmr) = read_sysreg_s(SYS_FPMR);
+}
+
 
 /*
  * We trap the first access to the FP/SIMD to save the host context and
@@ -425,7 +446,7 @@ 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 (host_owns_fp_regs())
+	if (is_protected_kvm_enabled() && host_owns_fp_regs())
 		kvm_hyp_save_fpsimd_host(vcpu);
 
 	/* Restore the guest state */

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

@@ -83,7 +83,7 @@ static void fpsimd_sve_sync(struct kvm_vcpu *vcpu)
 	if (system_supports_sve())
 		__hyp_sve_restore_host();
 	else
-		__fpsimd_restore_state(*host_data_ptr(fpsimd_state));
+		__fpsimd_restore_state(host_data_ptr(host_ctxt.fp_regs));
 
 	if (has_fpmr)
 		write_sysreg_s(*host_data_ptr(fpmr), SYS_FPMR);

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

@@ -192,34 +192,6 @@ static bool kvm_handle_pvm_sys64(struct kvm_vcpu *vcpu, u64 *exit_code)
 		kvm_handle_pvm_sysreg(vcpu, exit_code));
 }
 
-static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu)
-{
-	/*
-	 * Non-protected kvm relies on the host restoring its sve state.
-	 * Protected kvm restores the host's sve state as not to reveal that
-	 * fpsimd was used by a guest nor leak upper sve bits.
-	 */
-	if (unlikely(is_protected_kvm_enabled() && system_supports_sve())) {
-		__hyp_sve_save_host();
-
-		/* Re-enable SVE traps if not supported for the guest vcpu. */
-		if (!vcpu_has_sve(vcpu))
-			cpacr_clear_set(CPACR_EL1_ZEN, 0);
-
-	} 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[] = {
 	[0 ... ESR_ELx_EC_MAX]		= NULL,
 	[ESR_ELx_EC_CP15_32]		= kvm_hyp_handle_cp15_32,

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

@@ -413,14 +413,6 @@ static bool kvm_hyp_handle_eret(struct kvm_vcpu *vcpu, u64 *exit_code)
 	return true;
 }
 
-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)
 {
 	int ret = -EINVAL;