KVM: x86: Rename KVM_MSR_RET_INVALID to KVM_MSR_RET_UNSUPPORTED

Rename the "INVALID" internal MSR error return code to "UNSUPPORTED" to
try and make it more clear that access was denied because the MSR itself
is unsupported/unknown.  "INVALID" is too ambiguous, as it could just as
easily mean the value for WRMSR as invalid.

Avoid UNKNOWN and UNIMPLEMENTED, as the error code is used for MSRs that
_are_ actually implemented by KVM, e.g. if the MSR is unsupported because
an associated feature flag is not present in guest CPUID.

Opportunistically beef up the comments for the internal MSR error codes.

Link: https://lore.kernel.org/r/20240802181935.292540-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index eaa41a6a00ee6addab990f25fc1de8f96b509495..a265f6e621fcc5c444a938041068a2fd3cae528c 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2835,7 +2835,7 @@ static int svm_get_msr_feature(struct kvm_msr_entry *msr)
                        msr->data |= MSR_AMD64_DE_CFG_LFENCE_SERIALIZE;
                break;
        default:
-               return KVM_MSR_RET_INVALID;
+               return KVM_MSR_RET_UNSUPPORTED;
        }
 
        return 0;

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f18c2d8c7476e180005cef514953ab0e2ecb80bb..e5b253e4d421577a654401318d694bdd57f7ea38 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2006,7 +2006,7 @@ int vmx_get_msr_feature(struct kvm_msr_entry *msr)
                        return 1;
                return vmx_get_vmx_msr(&vmcs_config.nested, msr->index, &msr->data);
        default:
-               return KVM_MSR_RET_INVALID;
+               return KVM_MSR_RET_UNSUPPORTED;
        }
 }
 

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ffdf251bfef5b14daeaddcff782544950f5f2980..ea2f3ff93957473d3c8fed7610abd1b266b87dd5 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1687,7 +1687,7 @@ static int do_get_msr_feature(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
        msr.index = index;
        r = kvm_get_msr_feature(&msr);
 
-       if (r == KVM_MSR_RET_INVALID && kvm_msr_ignored_check(index, 0, false))
+       if (r == KVM_MSR_RET_UNSUPPORTED && kvm_msr_ignored_check(index, 0, false))
                r = 0;
 
        *data = msr.data;
@@ -1884,7 +1884,7 @@ static int kvm_set_msr_ignored_check(struct kvm_vcpu *vcpu,
 {
        int ret = __kvm_set_msr(vcpu, index, data, host_initiated);
 
-       if (ret == KVM_MSR_RET_INVALID)
+       if (ret == KVM_MSR_RET_UNSUPPORTED)
                if (kvm_msr_ignored_check(index, data, true))
                        ret = 0;
 
@@ -1929,7 +1929,7 @@ static int kvm_get_msr_ignored_check(struct kvm_vcpu *vcpu,
 {
        int ret = __kvm_get_msr(vcpu, index, data, host_initiated);
 
-       if (ret == KVM_MSR_RET_INVALID) {
+       if (ret == KVM_MSR_RET_UNSUPPORTED) {
                /* Unconditionally clear *data for simplicity */
                *data = 0;
                if (kvm_msr_ignored_check(index, 0, false))
@@ -1998,7 +1998,7 @@ static int complete_fast_rdmsr(struct kvm_vcpu *vcpu)
 static u64 kvm_msr_reason(int r)
 {
        switch (r) {
-       case KVM_MSR_RET_INVALID:
+       case KVM_MSR_RET_UNSUPPORTED:
                return KVM_MSR_EXIT_REASON_UNKNOWN;
        case KVM_MSR_RET_FILTERED:
                return KVM_MSR_EXIT_REASON_FILTER;
@@ -4146,7 +4146,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                    kvm_is_msr_to_save(msr))
                        break;
 
-               return KVM_MSR_RET_INVALID;
+               return KVM_MSR_RET_UNSUPPORTED;
        }
        return 0;
 }
@@ -4507,7 +4507,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                        break;
                }
 
-               return KVM_MSR_RET_INVALID;
+               return KVM_MSR_RET_UNSUPPORTED;
        }
        return 0;
 }

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 499adef960385d0b82f1bbb8732e73a5fb6dd6a9..f47b9905ba78253f478a9c7592b369c78601af8b 100644 (file)
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -512,11 +512,18 @@ enum kvm_msr_access {
 
 /*
  * Internal error codes that are used to indicate that MSR emulation encountered
- * an error that should result in #GP in the guest, unless userspace
- * handles it.
+ * an error that should result in #GP in the guest, unless userspace handles it.
+ * Note, '1', '0', and negative numbers are off limits, as they are used by KVM
+ * as part of KVM's lightly documented internal KVM_RUN return codes.
+ *
+ * UNSUPPORTED - The MSR isn't supported, either because it is completely
+ *               unknown to KVM, or because the MSR should not exist according
+ *               to the vCPU model.
+ *
+ * FILTERED    - Access to the MSR is denied by a userspace MSR filter.
  */
-#define  KVM_MSR_RET_INVALID   2       /* in-kernel MSR emulation #GP condition */
-#define  KVM_MSR_RET_FILTERED  3       /* #GP due to userspace MSR filter */
+#define  KVM_MSR_RET_UNSUPPORTED       2
+#define  KVM_MSR_RET_FILTERED          3
 
 #define __cr4_reserved_bits(__cpu_has, __c)             \
 ({                                                      \