[PATCH 4/6] KVM: SVM: Switch svm_copy_lbrs() to a macro

Yosry Ahmed
2025-11-08T00:45:59Z

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 c81005b245222..e7861392f2fcd 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -676,10 +676,12 @@ 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);
}
@@ -1186,10 +1188,12 @@ 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 fc42bcdbb5200..9eb112f0e61f0 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 c2acaa49ee1c5..e510c8183bd87 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