Commit 9ae7f6c9 authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
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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: default avatarWanpeng Li <wanpengli@tencent.com>
Message-Id: <1634724836-73721-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 9dadfc4a

arch/x86/kvm/emulate.c

+5 −0
Original line number Diff line number Diff line
@@ -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);