On 23/02/21 17:38, Sean Christopherson wrote:
On Tue, Feb 23, 2021, Like Xu wrote:
When the processor that support model-specific LBR generates a debug
breakpoint event, it automatically clears the LBR flag. This action
does not clear previously stored LBR stack MSRs. (Intel SDM 17.4.2)
Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
---
arch/x86/kvm/vmx/vmx.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index e0a3a9be654b..4951b535eb7f 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4795,6 +4795,7 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
u32 intr_info, ex_no, error_code;
unsigned long cr2, rip, dr6;
u32 vect_info;
+ u64 lbr_ctl;
vect_info = vmx->idt_vectoring_info;
intr_info = vmx_get_intr_info(vcpu);
@@ -4886,6 +4887,10 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
rip = kvm_rip_read(vcpu);
kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip;
kvm_run->debug.arch.exception = ex_no;
+ /* On the debug breakpoint event, the LBREn bit is cleared. */
Except this code is in BP_VECTOR, not DB_VECTOR as it should be.
When the processor generates a debug exception (#DB), it automatically clears
the LBR flag before executing the exception handler. This action does not
clear previously stored LBR stack MSRs.
Also, this should come with a testcase.
Paolo
