KVM: arm64: Relax trapping of CTR_EL0 when FEAT_EVT is available

CTR_EL0 can often be used in userspace, and it would be nice if
KVM didn't have to emulate it unnecessarily.

While it isn't possible to trap the cache configuration registers
independently from CTR_EL0 in the base ARMv8.0 architecture, FEAT_EVT
allows these cache configuration registers (CCSIDR_EL1, CCSIDR2_EL1,
CLIDR_EL1 and CSSELR_EL1) to be trapped independently by setting
HCR_EL2.TID4.

Switch to using TID4 instead of TID2 in the cases where FEAT_EVT
is available *and* that KVM doesn't need to sanitise CTR_EL0 to
paper over mismatched cache configurations.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230515170016.965378-1-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: Marc Zyngier

arch/arm64/include/asm/kvm_arm.h

@@ -18,6 +18,7 @@
 #define HCR_ATA_SHIFT	56
 #define HCR_ATA		(UL(1) << HCR_ATA_SHIFT)
 #define HCR_AMVOFFEN	(UL(1) << 51)
+#define HCR_TID4	(UL(1) << 49)
 #define HCR_FIEN	(UL(1) << 47)
 #define HCR_FWB		(UL(1) << 46)
 #define HCR_API		(UL(1) << 41)
@@ -86,7 +87,7 @@
 #define HCR_GUEST_FLAGS (HCR_TSC | HCR_TSW | HCR_TWE | HCR_TWI | HCR_VM | \
 			 HCR_BSU_IS | HCR_FB | HCR_TACR | \
 			 HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW | HCR_TLOR | \
-			 HCR_FMO | HCR_IMO | HCR_PTW | HCR_TID3 | HCR_TID2)
+			 HCR_FMO | HCR_IMO | HCR_PTW | HCR_TID3)
 #define HCR_VIRT_EXCP_MASK (HCR_VSE | HCR_VI | HCR_VF)
 #define HCR_HOST_NVHE_FLAGS (HCR_RW | HCR_API | HCR_APK | HCR_ATA)
 #define HCR_HOST_NVHE_PROTECTED_FLAGS (HCR_HOST_NVHE_FLAGS | HCR_TSC)

arch/arm64/include/asm/kvm_emulate.h

@@ -95,6 +95,12 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
 		vcpu->arch.hcr_el2 |= HCR_TVM;
 	}
 
+	if (cpus_have_final_cap(ARM64_HAS_EVT) &&
+	    !cpus_have_final_cap(ARM64_MISMATCHED_CACHE_TYPE))
+		vcpu->arch.hcr_el2 |= HCR_TID4;
+	else
+		vcpu->arch.hcr_el2 |= HCR_TID2;
+
 	if (vcpu_el1_is_32bit(vcpu))
 		vcpu->arch.hcr_el2 &= ~HCR_RW;
 

arch/arm64/kernel/cpufeature.c

@@ -2641,6 +2641,17 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.cpu_enable = cpu_enable_dit,
 		ARM64_CPUID_FIELDS(ID_AA64PFR0_EL1, DIT, IMP)
 	},
+	{
+		.desc = "Enhanced Virtualization Traps",
+		.capability = ARM64_HAS_EVT,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.sys_reg = SYS_ID_AA64MMFR2_EL1,
+		.sign = FTR_UNSIGNED,
+		.field_pos = ID_AA64MMFR2_EL1_EVT_SHIFT,
+		.field_width = 4,
+		.min_field_value = ID_AA64MMFR2_EL1_EVT_IMP,
+		.matches = has_cpuid_feature,
+	},
 	{},
 };
 

arch/arm64/tools/cpucaps

@@ -25,6 +25,7 @@ HAS_E0PD
 HAS_ECV
 HAS_ECV_CNTPOFF
 HAS_EPAN
+HAS_EVT
 HAS_GENERIC_AUTH
 HAS_GENERIC_AUTH_ARCH_QARMA3
 HAS_GENERIC_AUTH_ARCH_QARMA5