[PATCH -v5.1] x86/kvm: Implement HWCR support

[Borislav Petkov]

Hi all,

ok here's v5.1 with most of Sean's feedback addressed. The function
checking whether HWCR[18] is set, I've renamed to can_set_mci_status()
and left it to return bool because it really is used in boolean context,
answering the question "Can I set MCi_STATUS MSRs?"

And now it all looks simple and clean, just how I like it! :-)

Thx.

---
From: Borislav Petkov <bp@xxxxxxx>

The hardware configuration register has some useful bits which can be
used by guests. Implement McStatusWrEn which can be used by guests when
injecting MCEs with the in-kernel mce-inject module.

For that, we need to set bit 18 - McStatusWrEn - first, before writing
the MCi_STATUS registers (otherwise we #GP).

Add the required machinery to do so.

Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Jim Mattson <jmattson@xxxxxxxxxx>
Cc: Joerg Roedel <joro@xxxxxxxxxx>
Cc: KVM <kvm@xxxxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Yazen Ghannam <Yazen.Ghannam@xxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  3 +++
 arch/x86/kvm/x86.c              | 33 +++++++++++++++++++++++++++------
 2 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 159b5988292f..541c431df806 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -780,6 +780,9 @@ struct kvm_vcpu_arch {
 
 	/* Flush the L1 Data cache for L1TF mitigation on VMENTER */
 	bool l1tf_flush_l1d;
+
+	/* AMD MSRC001_0015 Hardware Configuration */
+	u64 msr_hwcr;
 };
 
 struct kvm_lpage_info {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 099b851dabaf..10f6acc6494c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2273,6 +2273,18 @@ static void kvmclock_sync_fn(struct work_struct *work)
 					KVMCLOCK_SYNC_PERIOD);
 }
 
+/*
+ * On AMD, HWCR[McStatusWrEn] controls whether setting MCi_STATUS results in #GP.
+ */
+static bool can_set_mci_status(struct kvm_vcpu *vcpu)
+{
+	/* McStatusWrEn enabled? */
+	if (guest_cpuid_is_amd(vcpu))
+		return !!(vcpu->arch.msr_hwcr & BIT_ULL(18));
+
+	return false;
+}
+
 static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
 	u64 mcg_cap = vcpu->arch.mcg_cap;
@@ -2304,9 +2316,13 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			if ((offset & 0x3) == 0 &&
 			    data != 0 && (data | (1 << 10)) != ~(u64)0)
 				return -1;
-			if (!msr_info->host_initiated &&
-				(offset & 0x3) == 1 && data != 0)
-				return -1;
+
+			/* MCi_STATUS */
+			if ((offset & 0x3) == 1 && !msr_info->host_initiated) {
+				if (!can_set_mci_status(vcpu))
+					return -1;
+			}
+
 			vcpu->arch.mce_banks[offset] = data;
 			break;
 		}
@@ -2455,8 +2471,11 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		data &= ~(u64)0x40;	/* ignore flush filter disable */
 		data &= ~(u64)0x100;	/* ignore ignne emulation enable */
 		data &= ~(u64)0x8;	/* ignore TLB cache disable */
-		data &= ~(u64)0x40000;  /* ignore Mc status write enable */
-		if (data != 0) {
+
+		/* Handle McStatusWrEn */
+		if (data == BIT_ULL(18)) {
+			vcpu->arch.msr_hwcr = data;
+		} else if (data != 0) {
 			vcpu_unimpl(vcpu, "unimplemented HWCR wrmsr: 0x%llx\n",
 				    data);
 			return 1;
@@ -2730,7 +2749,6 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_K8_SYSCFG:
 	case MSR_K8_TSEG_ADDR:
 	case MSR_K8_TSEG_MASK:
-	case MSR_K7_HWCR:
 	case MSR_VM_HSAVE_PA:
 	case MSR_K8_INT_PENDING_MSG:
 	case MSR_AMD64_NB_CFG:
@@ -2894,6 +2912,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_MISC_FEATURES_ENABLES:
 		msr_info->data = vcpu->arch.msr_misc_features_enables;
 		break;
+	case MSR_K7_HWCR:
+		msr_info->data = vcpu->arch.msr_hwcr;
+		break;
 	default:
 		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
 			return kvm_pmu_get_msr(vcpu, msr_info->index, &msr_info->data);
-- 
2.21.0

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.