KVM: arm64/sve: System register context switch and access support

This patch adds the necessary support for context switching ZCR_EL1
for each vcpu.

ZCR_EL1 is trapped alongside the FPSIMD/SVE registers, so it makes
sense for it to be handled as part of the guest FPSIMD/SVE context
for context switch purposes instead of handling it as a general
system register.  This means that it can be switched in lazily at
the appropriate time.  No effort is made to track host context for
this register, since SVE requires VHE: thus the hosts's value for
this register lives permanently in ZCR_EL2 and does not alias the
guest's value at any time.

The Hyp switch and fpsimd context handling code is extended
appropriately.

Accessors are added in sys_regs.c to expose the SVE system
registers and ID register fields.  Because these need to be
conditionally visible based on the guest configuration, they are
implemented separately for now rather than by use of the generic
system register helpers.  This may be abstracted better later on
when/if there are more features requiring this model.

ID_AA64ZFR0_EL1 is RO-RAZ for MRS/MSR when SVE is disabled for the
guest, but for compatibility with non-SVE aware KVM implementations
the register should not be enumerated at all for KVM_GET_REG_LIST
in this case.  For consistency we also reject ioctl access to the
register.  This ensures that a non-SVE-enabled guest looks the same
to userspace, irrespective of whether the kernel KVM implementation
supports SVE.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Tested-by: zhang.lei <zhang.lei@jp.fujitsu.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/include/asm/kvm_host.h

@@ -121,6 +121,7 @@ enum vcpu_sysreg {
 	SCTLR_EL1,	/* System Control Register */
 	ACTLR_EL1,	/* Auxiliary Control Register */
 	CPACR_EL1,	/* Coprocessor Access Control */
+	ZCR_EL1,	/* SVE Control */
 	TTBR0_EL1,	/* Translation Table Base Register 0 */
 	TTBR1_EL1,	/* Translation Table Base Register 1 */
 	TCR_EL1,	/* Translation Control Register */

arch/arm64/include/asm/sysreg.h

@@ -454,6 +454,9 @@
 #define SYS_ICH_LR14_EL2		__SYS__LR8_EL2(6)
 #define SYS_ICH_LR15_EL2		__SYS__LR8_EL2(7)
 
+/* VHE encodings for architectural EL0/1 system registers */
+#define SYS_ZCR_EL12			sys_reg(3, 5, 1, 2, 0)
+
 /* Common SCTLR_ELx flags. */
 #define SCTLR_ELx_DSSBS	(_BITUL(44))
 #define SCTLR_ELx_ENIA	(_BITUL(31))

arch/arm64/kvm/fpsimd.c

@@ -103,14 +103,21 @@ void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
 void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
 {
 	unsigned long flags;
+	bool host_has_sve = system_supports_sve();
+	bool guest_has_sve = vcpu_has_sve(vcpu);
 
 	local_irq_save(flags);
 
 	if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
+		u64 *guest_zcr = &vcpu->arch.ctxt.sys_regs[ZCR_EL1];
+
 		/* Clean guest FP state to memory and invalidate cpu view */
 		fpsimd_save();
 		fpsimd_flush_cpu_state();
-	} else if (system_supports_sve()) {
+
+		if (guest_has_sve)
+			*guest_zcr = read_sysreg_s(SYS_ZCR_EL12);
+	} else if (host_has_sve) {
 		/*
 		 * The FPSIMD/SVE state in the CPU has not been touched, and we
 		 * have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been

arch/arm64/kvm/hyp/switch.c

@@ -351,6 +351,9 @@ static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu)
 
 	__fpsimd_restore_state(&vcpu->arch.ctxt.gp_regs.fp_regs);
 
+	if (vcpu_has_sve(vcpu))
+		write_sysreg_s(vcpu->arch.ctxt.sys_regs[ZCR_EL1], SYS_ZCR_EL12);
+
 	/* Skip restoring fpexc32 for AArch64 guests */
 	if (!(read_sysreg(hcr_el2) & HCR_RW))
 		write_sysreg(vcpu->arch.ctxt.sys_regs[FPEXC32_EL2],

arch/arm64/kvm/sys_regs.c

@@ -1051,10 +1051,7 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 			 (u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
 	u64 val = raz ? 0 : read_sanitised_ftr_reg(id);
 
-	if (id == SYS_ID_AA64PFR0_EL1) {
-		if (val & (0xfUL << ID_AA64PFR0_SVE_SHIFT))
-			kvm_debug("SVE unsupported for guests, suppressing\n");
-
+	if (id == SYS_ID_AA64PFR0_EL1 && !vcpu_has_sve(vcpu)) {
 		val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
 	} else if (id == SYS_ID_AA64ISAR1_EL1) {
 		const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) |
@@ -1101,6 +1098,81 @@ static int reg_from_user(u64 *val, const void __user *uaddr, u64 id);
 static int reg_to_user(void __user *uaddr, const u64 *val, u64 id);
 static u64 sys_reg_to_index(const struct sys_reg_desc *reg);
 
+/* Visibility overrides for SVE-specific control registers */
+static unsigned int sve_visibility(const struct kvm_vcpu *vcpu,
+				   const struct sys_reg_desc *rd)
+{
+	if (vcpu_has_sve(vcpu))
+		return 0;
+
+	return REG_HIDDEN_USER | REG_HIDDEN_GUEST;
+}
+
+/* Visibility overrides for SVE-specific ID registers */
+static unsigned int sve_id_visibility(const struct kvm_vcpu *vcpu,
+				      const struct sys_reg_desc *rd)
+{
+	if (vcpu_has_sve(vcpu))
+		return 0;
+
+	return REG_HIDDEN_USER;
+}
+
+/* Generate the emulated ID_AA64ZFR0_EL1 value exposed to the guest */
+static u64 guest_id_aa64zfr0_el1(const struct kvm_vcpu *vcpu)
+{
+	if (!vcpu_has_sve(vcpu))
+		return 0;
+
+	return read_sanitised_ftr_reg(SYS_ID_AA64ZFR0_EL1);
+}
+
+static bool access_id_aa64zfr0_el1(struct kvm_vcpu *vcpu,
+				   struct sys_reg_params *p,
+				   const struct sys_reg_desc *rd)
+{
+	if (p->is_write)
+		return write_to_read_only(vcpu, p, rd);
+
+	p->regval = guest_id_aa64zfr0_el1(vcpu);
+	return true;
+}
+
+static int get_id_aa64zfr0_el1(struct kvm_vcpu *vcpu,
+		const struct sys_reg_desc *rd,
+		const struct kvm_one_reg *reg, void __user *uaddr)
+{
+	u64 val;
+
+	if (!vcpu_has_sve(vcpu))
+		return -ENOENT;
+
+	val = guest_id_aa64zfr0_el1(vcpu);
+	return reg_to_user(uaddr, &val, reg->id);
+}
+
+static int set_id_aa64zfr0_el1(struct kvm_vcpu *vcpu,
+		const struct sys_reg_desc *rd,
+		const struct kvm_one_reg *reg, void __user *uaddr)
+{
+	const u64 id = sys_reg_to_index(rd);
+	int err;
+	u64 val;
+
+	if (!vcpu_has_sve(vcpu))
+		return -ENOENT;
+
+	err = reg_from_user(&val, uaddr, id);
+	if (err)
+		return err;
+
+	/* This is what we mean by invariant: you can't change it. */
+	if (val != guest_id_aa64zfr0_el1(vcpu))
+		return -EINVAL;
+
+	return 0;
+}
+
 /*
  * cpufeature ID register user accessors
  *
@@ -1346,7 +1418,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	ID_SANITISED(ID_AA64PFR1_EL1),
 	ID_UNALLOCATED(4,2),
 	ID_UNALLOCATED(4,3),
-	ID_UNALLOCATED(4,4),
+	{ SYS_DESC(SYS_ID_AA64ZFR0_EL1), access_id_aa64zfr0_el1, .get_user = get_id_aa64zfr0_el1, .set_user = set_id_aa64zfr0_el1, .visibility = sve_id_visibility },
 	ID_UNALLOCATED(4,5),
 	ID_UNALLOCATED(4,6),
 	ID_UNALLOCATED(4,7),
@@ -1383,6 +1455,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 
 	{ SYS_DESC(SYS_SCTLR_EL1), access_vm_reg, reset_val, SCTLR_EL1, 0x00C50078 },
 	{ SYS_DESC(SYS_CPACR_EL1), NULL, reset_val, CPACR_EL1, 0 },
+	{ SYS_DESC(SYS_ZCR_EL1), NULL, reset_val, ZCR_EL1, 0, .visibility = sve_visibility },
 	{ SYS_DESC(SYS_TTBR0_EL1), access_vm_reg, reset_unknown, TTBR0_EL1 },
 	{ SYS_DESC(SYS_TTBR1_EL1), access_vm_reg, reset_unknown, TTBR1_EL1 },
 	{ SYS_DESC(SYS_TCR_EL1), access_vm_reg, reset_val, TCR_EL1, 0 },