On 5/30/25 01:39, Sean Christopherson wrote:
Use a dedicated array of MSRPM offsets to merge L0 and L1 bitmaps, i.e. to
merge KVM's vmcb01 bitmap with L1's vmcb12 bitmap. This will eventually
allow for the removal of direct_access_msrs, as the only path where
tracking the offsets is truly justified is the merge for nested SVM, where
merging in chunks is an easy way to batch uaccess reads/writes.
Opportunistically omit the x2APIC MSRs from the merge-specific array
instead of filtering them out at runtime.
Note, disabling interception of XSS, EFER, PAT, GHCB, and TSC_AUX is
mutually exclusive with nested virtualization, as KVM passes through the
MSRs only for SEV-ES guests, and KVM doesn't support nested virtualization
for SEV+ guests. Defer removing those MSRs to a future cleanup in order
to make this refactoring as benign as possible.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/svm/nested.c | 72 +++++++++++++++++++++++++++++++++------
arch/x86/kvm/svm/svm.c | 4 +++
arch/x86/kvm/svm/svm.h | 2 ++
3 files changed, 67 insertions(+), 11 deletions(-)
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 89a77f0f1cc8..e53020939e60 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -184,6 +184,64 @@ void recalc_intercepts(struct vcpu_svm *svm)
}
}
+static int nested_svm_msrpm_merge_offsets[9] __ro_after_init;
+static int nested_svm_nr_msrpm_merge_offsets __ro_after_init;
+
+int __init nested_svm_init_msrpm_merge_offsets(void)
+{
+ const u32 merge_msrs[] = {
"static const", please.
Paolo
+ MSR_STAR,
+ MSR_IA32_SYSENTER_CS,
+ MSR_IA32_SYSENTER_EIP,
+ MSR_IA32_SYSENTER_ESP,
+ #ifdef CONFIG_X86_64
+ MSR_GS_BASE,
+ MSR_FS_BASE,
+ MSR_KERNEL_GS_BASE,
+ MSR_LSTAR,
+ MSR_CSTAR,
+ MSR_SYSCALL_MASK,
+ #endif
+ MSR_IA32_SPEC_CTRL,
+ MSR_IA32_PRED_CMD,
+ MSR_IA32_FLUSH_CMD,
+ MSR_IA32_LASTBRANCHFROMIP,
+ MSR_IA32_LASTBRANCHTOIP,
+ MSR_IA32_LASTINTFROMIP,
+ MSR_IA32_LASTINTTOIP,
+
+ MSR_IA32_XSS,
+ MSR_EFER,
+ MSR_IA32_CR_PAT,
+ MSR_AMD64_SEV_ES_GHCB,
+ MSR_TSC_AUX,
+ };
+ int i, j;
+
+ for (i = 0; i < ARRAY_SIZE(merge_msrs); i++) {
+ u32 offset = svm_msrpm_offset(merge_msrs[i]);
+
+ if (WARN_ON(offset == MSR_INVALID))
+ return -EIO;
+
+ for (j = 0; j < nested_svm_nr_msrpm_merge_offsets; j++) {
+ if (nested_svm_msrpm_merge_offsets[j] == offset)
+ break;
+ }
+
+ if (j < nested_svm_nr_msrpm_merge_offsets)
+ continue;
+
+ if (WARN_ON(j >= ARRAY_SIZE(nested_svm_msrpm_merge_offsets)))
+ return -EIO;
+
+ nested_svm_msrpm_merge_offsets[j] = offset;
+ nested_svm_nr_msrpm_merge_offsets++;
+ }
+
+ return 0;
+}
+
/*
* Merge L0's (KVM) and L1's (Nested VMCB) MSR permission bitmaps. The function
* is optimized in that it only merges the parts where KVM MSR permission bitmap
@@ -216,19 +274,11 @@ static bool nested_svm_merge_msrpm(struct kvm_vcpu *vcpu)
if (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT)))
return true;
- for (i = 0; i < MSRPM_OFFSETS; i++) {
- u32 value, p;
+ for (i = 0; i < nested_svm_nr_msrpm_merge_offsets; i++) {
+ const int p = nested_svm_msrpm_merge_offsets[i];
+ u32 value;
u64 offset;
- if (msrpm_offsets[i] == 0xffffffff)
- break;
-
- p = msrpm_offsets[i];
-
- /* x2apic msrs are intercepted always for the nested guest */
- if (is_x2apic_msrpm_offset(p))
- continue;
-
offset = svm->nested.ctl.msrpm_base_pa + (p * 4);
if (kvm_vcpu_read_guest(vcpu, offset, &value, 4))
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 1c70293400bc..84dd1f220986 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5689,6 +5689,10 @@ static int __init svm_init(void)
if (!kvm_is_svm_supported())
return -EOPNOTSUPP;
+ r = nested_svm_init_msrpm_merge_offsets();
+ if (r)
+ return r;
+
r = kvm_x86_vendor_init(&svm_init_ops);
if (r)
return r;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 909b9af6b3c1..0a8041d70994 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -686,6 +686,8 @@ static inline bool nested_exit_on_nmi(struct vcpu_svm *svm)
return vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_NMI);
}
+int __init nested_svm_init_msrpm_merge_offsets(void);
+
int enter_svm_guest_mode(struct kvm_vcpu *vcpu,
u64 vmcb_gpa, struct vmcb *vmcb12, bool from_vmrun);
void svm_leave_nested(struct kvm_vcpu *vcpu);
