From 9ae7f6c9b51e297a7f5c2eb8ff5de42f8402eb71 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Wed, 20 Oct 2021 03:13:56 -0700 Subject: KVM: emulate: Comment on difference between RDPMC implementation and manual 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. Signed-off-by: Wanpeng Li Message-Id: <1634724836-73721-1-git-send-email-wanpengli@tencent.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/emulate.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'arch/x86/kvm/emulate.c') diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index c589ac832265..532791ffcbb9 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4223,6 +4223,11 @@ static int check_rdpmc(struct x86_emulate_ctxt *ctxt) if (enable_vmware_backdoor && is_vmware_backdoor_pmc(rcx)) return X86EMUL_CONTINUE; + /* + * If CR4.PCE is set, the SDM requires CPL=0 or CR0.PE=0. The CR0.PE + * check however is unnecessary because CPL is always 0 outside + * protected mode. + */ if ((!(cr4 & X86_CR4_PCE) && ctxt->ops->cpl(ctxt)) || ctxt->ops->check_pmc(ctxt, rcx)) return emulate_gp(ctxt, 0); -- cgit v1.2.3-59-g8ed1b