KVM: Ignore DEBUGCTL MSRs with no effect

Netware writes to DEBUGCTL and reads from the DEBUGCTL and LAST*IP MSRs
without further checks and is really confused to receive a #GP during that.
To make it happy we should just make them stubs, which is exactly what SVM
already does.

Writes to DEBUGCTL that are vendor-specific are resembled to behave as if the
virtual CPU does not know them.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5620df2685db..94a216562f10 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -665,6 +665,18 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
                 pr_unimpl(vcpu, "%s: MSR_IA32_MCG_CTL 0x%llx, nop\n",
                         __func__, data);
                 break;
+        case MSR_IA32_DEBUGCTLMSR:
+                if (!data) {
+                        /* We support the non-activated case already */
+                        break;
+                } else if (data & ~(DEBUGCTLMSR_LBR | DEBUGCTLMSR_BTF)) {
+                        /* Values other than LBR and BTF are vendor-specific,
+                           thus reserved and should throw a #GP */
+                        return 1;
+                }
+                pr_unimpl(vcpu, "%s: MSR_IA32_DEBUGCTLMSR 0x%llx, nop\n",
+                        __func__, data);
+                break;
         case MSR_IA32_UCODE_REV:
         case MSR_IA32_UCODE_WRITE:
                 break;
@@ -757,6 +769,11 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
         case MSR_IA32_MC0_MISC+16:
         case MSR_IA32_UCODE_REV:
         case MSR_IA32_EBL_CR_POWERON:
+        case MSR_IA32_DEBUGCTLMSR:
+        case MSR_IA32_LASTBRANCHFROMIP:
+        case MSR_IA32_LASTBRANCHTOIP:
+        case MSR_IA32_LASTINTFROMIP:
+        case MSR_IA32_LASTINTTOIP:
                 data = 0;
                 break;
         case MSR_MTRRcap: