[PATCH v3 2/2] x86/kvm: Implement MSR_HWCR support

[Borislav Petkov]

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>
Tested-by: Yazen Ghannam <yazen.ghannam@xxxxxxx>
---
 arch/x86/kvm/svm.c | 12 +++++++++---
 arch/x86/kvm/x86.c | 34 +++++++++++++++++++++++++++++++---
 2 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5c9c26dc7d84..db8e943f7576 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -251,6 +251,9 @@ struct vcpu_svm {
 
 	/* which host CPU was used for running this vcpu */
 	unsigned int last_cpu;
+
+	/* MSRC001_0015 Hardware Configuration */
+	u64 msr_hwcr;
 };
 
 /*
@@ -4155,7 +4158,7 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = svm->msr_decfg;
 		break;
 	case MSR_K7_HWCR:
-		msr_info->data = 0;
+		msr_info->data = svm->msr_hwcr;
 		break;
 	default:
 		return kvm_get_msr_common(vcpu, msr_info);
@@ -4365,8 +4368,11 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		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)) {
+			svm->msr_hwcr = data;
+		} else if (data != 0) {
 			vcpu_unimpl(vcpu, "unimplemented HWCR wrmsr: 0x%llx\n",
 				    data);
 			return 1;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d9abbe24deb5..607fe883113c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2262,6 +2262,30 @@ 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 __set_mci_status(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+{
+	if (guest_cpuid_is_amd(vcpu)) {
+		struct msr_data tmp;
+
+		tmp.index = MSR_K7_HWCR;
+
+		if (kvm_x86_ops->get_msr(vcpu, &tmp))
+			return false;
+
+		/* McStatusWrEn enabled? */
+		if (tmp.data & BIT_ULL(18))
+			return true;
+	}
+
+	if (msr_info->data != 0)
+		return false;
+
+	return true;
+}
+
 static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
 	u64 mcg_cap = vcpu->arch.mcg_cap;
@@ -2293,9 +2317,13 @@ 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 (!__set_mci_status(vcpu, msr_info))
+						return -1;
+			}
+
 			vcpu->arch.mce_banks[offset] = data;
 			break;
 		}
-- 
2.19.1