From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
SDM mentioned that, RDPMC:
IF (((CR4.PCE = 1) or (CPL = 0) or (CR0.PE = 0)) and (ECX indicates a supported counter))
THEN
EAX := counter[31:0];
EDX := ZeroExtend(counter[MSCB:32]);
ELSE (* ECX is not valid or CR4.PCE is 0 and CPL is 1, 2, or 3 and CR0.PE is 1 *)
#GP(0);
FI;
Let's add a comment why CR0.PE isn't tested since it's impossible for CPL to be >0 if
CR0.PE=0.
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
---
v4 -> v5:
* just comments
v3 -> v4:
* add comments instead of pseudocode
v2 -> v3:
* add the missing 'S'
v1 -> v2:
* update patch description
arch/x86/kvm/emulate.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 9a144ca8e146..c289809beea3 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4222,6 +4222,9 @@ static int check_rdpmc(struct x86_emulate_ctxt *ctxt)
if (enable_vmware_backdoor && is_vmware_backdoor_pmc(rcx))
return X86EMUL_CONTINUE;
+ /*
+ * It's impossible for CPL to be >0 if CR0.PE=0.
+ */
if ((!(cr4 & X86_CR4_PCE) && ctxt->ops->cpl(ctxt)) ||
ctxt->ops->check_pmc(ctxt, rcx))
return emulate_gp(ctxt, 0);
--
2.25.1
