[PATCH v4 17/27] KVM: arm64: Support SME identification registers for guests

[Mark Brown <broonie@kernel.org>]

The primary register for identifying SME is ID_AA64PFR1_EL1.SME.  This
is hidden from guests unless SME is enabled by the VMM.
When it is visible it is writable and can be used to control the
availability of SME2.

There is also a new register ID_AA64SMFR0_EL1 which we make writable,
forcing it to all bits 0 if SME is disabled.  This includes the field
SMEver giving the SME version, userspace is responsible for ensuring
the value is consistent with ID_AA64PFR1_EL1.SME.  It also includes
FA64, a separately enableable extension which provides the full FPSIMD
and SVE instruction set including FFR in streaming mode.  Userspace can
control the availability of FA64 by writing to this field.  The other
features enumerated there only add new instructions, there are no
architectural controls for these.

There is a further identification register SMIDR_EL1 which provides a
basic description of the SME microarchitecture, in a manner similar to
MIDR_EL1 for the PE.  It also describes support for priority management
and a basic affinity description for shared SME units, plus some RES0
space.  We do not support priority management and affinity is not
meaningful for guests so we mask out everything except for the
microarchitecture description.

As for MIDR_EL1 and REVIDR_EL1 we expose the implementer and revision
information to guests with the raw value from the CPU we are running on,
this may present issues for asymmetric systems or for migration as it
does for the existing registers.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/kvm_host.h |  1 +
 arch/arm64/kvm/sys_regs.c         | 46 +++++++++++++++++++++++++++++++++++----
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index c770ed6138164fcd3e11b8517ef4120b4f4486b9..14615216845668bf1a614e9fbdb6112190fec054 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -473,6 +473,7 @@ enum vcpu_sysreg {
 	/* FP/SIMD/SVE */
 	SVCR,
 	FPMR,
+	SMIDR_EL1,	/* Streaming Mode Identification Register */
 
 	/* 32bit specific registers. */
 	DACR32_EL2,	/* Domain Access Control Register */
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index eece67141480b8d4bbd2bac0f02f9208c7f86f8b..b515dfa1f27d0c744de996f6dcdff272aa184385 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -767,6 +767,38 @@ static u64 reset_mpidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 	return mpidr;
 }
 
+static u64 reset_smidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
+{
+	u64 smidr = 0;
+
+	if (!system_supports_sme())
+		return smidr;
+
+	smidr = read_sysreg_s(SYS_SMIDR_EL1);
+
+	/*
+	 * Mask out everything except for the implementer and revison,
+	 * in particular priority management is not implemented.
+	 */
+	smidr &= SMIDR_EL1_IMPLEMENTER_MASK | SMIDR_EL1_REVISION_MASK;
+
+	vcpu_write_sys_reg(vcpu, smidr, SMIDR_EL1);
+
+	return smidr;
+}
+
+static bool access_smidr(struct kvm_vcpu *vcpu,
+			 struct sys_reg_params *p,
+			 const struct sys_reg_desc *r)
+{
+	if (p->is_write)
+		return write_to_read_only(vcpu, p, r);
+
+	p->regval = vcpu_read_sys_reg(vcpu, r->reg);
+
+	return true;
+}
+
 static unsigned int pmu_visibility(const struct kvm_vcpu *vcpu,
 				   const struct sys_reg_desc *r)
 {
@@ -1593,7 +1625,9 @@ static u64 __kvm_read_sanitised_id_reg(const struct kvm_vcpu *vcpu,
 		if (!kvm_has_mte(vcpu->kvm))
 			val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MTE);
 
-		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_SME);
+		if (!vcpu_has_sme(vcpu))
+			val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_SME);
+
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_RNDR_trap);
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_NMI);
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MTE_frac);
@@ -1697,6 +1731,10 @@ static unsigned int id_visibility(const struct kvm_vcpu *vcpu,
 		if (!vcpu_has_sve(vcpu))
 			return REG_RAZ;
 		break;
+	case SYS_ID_AA64SMFR0_EL1:
+		if (!vcpu_has_sme(vcpu))
+			return REG_RAZ;
+		break;
 	}
 
 	return 0;
@@ -2637,7 +2675,6 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 				       ID_AA64PFR1_EL1_MTE_frac |
 				       ID_AA64PFR1_EL1_NMI |
 				       ID_AA64PFR1_EL1_RNDR_trap |
-				       ID_AA64PFR1_EL1_SME |
 				       ID_AA64PFR1_EL1_RES0 |
 				       ID_AA64PFR1_EL1_MPAM_frac |
 				       ID_AA64PFR1_EL1_RAS_frac |
@@ -2645,7 +2682,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	ID_WRITABLE(ID_AA64PFR2_EL1, ID_AA64PFR2_EL1_FPMR),
 	ID_UNALLOCATED(4,3),
 	ID_WRITABLE(ID_AA64ZFR0_EL1, ~ID_AA64ZFR0_EL1_RES0),
-	ID_HIDDEN(ID_AA64SMFR0_EL1),
+	ID_WRITABLE(ID_AA64SMFR0_EL1, ~ID_AA64SMFR0_EL1_RES0),
 	ID_UNALLOCATED(4,6),
 	ID_WRITABLE(ID_AA64FPFR0_EL1, ~ID_AA64FPFR0_EL1_RES0),
 
@@ -2845,7 +2882,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ SYS_DESC(SYS_CLIDR_EL1), access_clidr, reset_clidr, CLIDR_EL1,
 	  .set_user = set_clidr, .val = ~CLIDR_EL1_RES0 },
 	{ SYS_DESC(SYS_CCSIDR2_EL1), undef_access },
-	{ SYS_DESC(SYS_SMIDR_EL1), undef_access },
+	{ SYS_DESC(SYS_SMIDR_EL1), .access = access_smidr, .reset = reset_smidr,
+	  .reg = SMIDR_EL1, .visibility = sme_visibility },
 	{ SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown, CSSELR_EL1 },
 	ID_FILTERED(CTR_EL0, ctr_el0,
 		    CTR_EL0_DIC_MASK |

-- 
2.39.5