[PATCH v2 01/13] KVM: SVM: Switch svm_copy_lbrs() to a macro

Yosry Ahmed
2025-11-10T22:29:45Z

In preparation for using svm_copy_lbrs() with 'struct vmcb_save_area'
without a containing 'struct vmcb', and later even 'struct
vmcb_save_area_cached', make it a macro. Pull the call to
vmcb_mark_dirty() out to the callers.

Macros are generally not preferred compared to functions, mainly due to
type-safety. However, in this case it seems like having a simple macro
copying a few fields is better than copy-pasting the same 5 lines of
code in different places.

On the bright side, pulling vmcb_mark_dirty() calls to the callers makes
it clear that in one case, vmcb_mark_dirty() was being called on VMCB12.
It is not architecturally defined for the CPU to clear arbitrary clean
bits, and it is not needed, so drop that one call.

Technically fixes the non-architectural behavior of setting the dirty
bit on VMCB12.

Fixes: d20c796ca370 ("KVM: x86: nSVM: implement nested LBR virtualization")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
arch/x86/kvm/svm/nested.c | 16 ++++++++++------
arch/x86/kvm/svm/svm.c | 11 -----------
arch/x86/kvm/svm/svm.h | 10 +++++++++-
3 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index da6e80b3ac353..a37bd5c1f36fa 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -675,10 +675,12 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
* Reserved bits of DEBUGCTL are ignored. Be consistent with
* svm_set_msr's definition of reserved bits.
*/
- svm_copy_lbrs(vmcb02, vmcb12);
+ svm_copy_lbrs(&vmcb02->save, &vmcb12->save);
+ vmcb_mark_dirty(vmcb02, VMCB_LBR);
vmcb02->save.dbgctl &= ~DEBUGCTL_RESERVED_BITS;
} else {
- svm_copy_lbrs(vmcb02, vmcb01);
+ svm_copy_lbrs(&vmcb02->save, &vmcb01->save);
+ vmcb_mark_dirty(vmcb02, VMCB_LBR);
}
svm_update_lbrv(&svm->vcpu);
}
@@ -1184,10 +1186,12 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
kvm_make_request(KVM_REQ_EVENT, &svm->vcpu);

if (unlikely(guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV) &&
- (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK)))
- svm_copy_lbrs(vmcb12, vmcb02);
- else
- svm_copy_lbrs(vmcb01, vmcb02);
+ (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
+ svm_copy_lbrs(&vmcb12->save, &vmcb02->save);
+ } else {
+ svm_copy_lbrs(&vmcb01->save, &vmcb02->save);
+ vmcb_mark_dirty(vmcb01, VMCB_LBR);
+ }

svm_update_lbrv(vcpu);

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 10c21e4c5406f..711276e8ee84f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -795,17 +795,6 @@ static void svm_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
*/
}

-void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
-{
- to_vmcb->save.dbgctl = from_vmcb->save.dbgctl;
- to_vmcb->save.br_from = from_vmcb->save.br_from;
- to_vmcb->save.br_to = from_vmcb->save.br_to;
- to_vmcb->save.last_excp_from = from_vmcb->save.last_excp_from;
- to_vmcb->save.last_excp_to = from_vmcb->save.last_excp_to;
-
- vmcb_mark_dirty(to_vmcb, VMCB_LBR);
-}
-
static void __svm_enable_lbrv(struct kvm_vcpu *vcpu)
{
to_svm(vcpu)->vmcb->control.virt_ext |= LBR_CTL_ENABLE_MASK;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index c856d8e0f95e7..f6fb70ddf7272 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -687,8 +687,16 @@ static inline void *svm_vcpu_alloc_msrpm(void)
return svm_alloc_permissions_map(MSRPM_SIZE, GFP_KERNEL_ACCOUNT);
}

+#define svm_copy_lbrs(to, from) \
+({ \
+ (to)->dbgctl = (from)->dbgctl; \
+ (to)->br_from = (from)->br_from; \
+ (to)->br_to = (from)->br_to; \
+ (to)->last_excp_from = (from)->last_excp_from; \
+ (to)->last_excp_to = (from)->last_excp_to; \
+})
+
void svm_vcpu_free_msrpm(void *msrpm);
-void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb);
void svm_enable_lbrv(struct kvm_vcpu *vcpu);
void svm_update_lbrv(struct kvm_vcpu *vcpu);

--
2.51.2.1041.gc1ab5b90ca-goog