[PATCH] KVM: arm64: Relax trapping of CTR_EL0 when FEAT_EVT is available

* [PATCH] KVM: arm64: Relax trapping of CTR_EL0 when FEAT_EVT is available
@ 2023-05-15 17:00 Marc Zyngier
  2023-05-21 19:00 ` Oliver Upton
  2023-05-21 19:19 ` Oliver Upton
  0 siblings, 2 replies; 3+ messages in thread
From: Marc Zyngier @ 2023-05-15 17:00 UTC (permalink / raw)
  To: kvmarm, kvm, linux-arm-kernel
  Cc: James Morse, Suzuki K Poulose, Oliver Upton, Zenghui Yu

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
indemendently 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 indepdently 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>
---
 arch/arm64/include/asm/kvm_arm.h     |  2 +-
 arch/arm64/include/asm/kvm_emulate.h |  6 ++++++
 arch/arm64/kernel/cpufeature.c       | 11 +++++++++++
 arch/arm64/tools/cpucaps             |  1 +
 4 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
index baef29fcbeee..209a4fba5d2a 100644
--- a/arch/arm64/include/asm/kvm_arm.h
+++ b/arch/arm64/include/asm/kvm_arm.h
@@ -86,7 +86,7 @@
 #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)
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index b31b32ecbe2d..a08291051ac9 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/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;
 
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index c331c49a7d19..bd184c2cef33 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2783,6 +2783,17 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.matches = has_cpuid_feature,
 		.cpu_enable = cpu_enable_dit,
 	},
+	{
+		.desc = "Extended 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,
+	},
 	{},
 };
 
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 40ba95472594..606d1184a5e9 100644
--- a/arch/arm64/tools/cpucaps
+++ b/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
-- 
2.34.1


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