The shortlog makes it sound like "inject a #GP if CR0.PE=1", i.e. unconditionally
inject #GP for RDMPC in protected mode. Maybe "Don't inject #GP when emulating
RDMPC if CR0.PE=0"?
On Fri, Oct 08, 2021, Wanpeng Li wrote:
> 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 the CR0.PE is 1 checking to rdpmc emulate.
>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
> arch/x86/kvm/emulate.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 9a144ca8e146..ab7ec569e8c9 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -4213,6 +4213,7 @@ static int check_rdtsc(struct x86_emulate_ctxt *ctxt)
> static int check_rdpmc(struct x86_emulate_ctxt *ctxt)
> {
> u64 cr4 = ctxt->ops->get_cr(ctxt, 4);
> + u64 cr0 = ctxt->ops->get_cr(ctxt, 0);
> u64 rcx = reg_read(ctxt, VCPU_REGS_RCX);
>
> /*
> @@ -4222,7 +4223,7 @@ static int check_rdpmc(struct x86_emulate_ctxt *ctxt)
> if (enable_vmware_backdoor && is_vmware_backdoor_pmc(rcx))
> return X86EMUL_CONTINUE;
>
> - if ((!(cr4 & X86_CR4_PCE) && ctxt->ops->cpl(ctxt)) ||
> + if ((!(cr4 & X86_CR4_PCE) && ctxt->ops->cpl(ctxt) && (cr0 & X86_CR0_PE)) ||
I don't think it's possible for CPL to be >0 if CR0.PE=0, e.g. we could probably
WARN in the #GP path. Realistically it doesn't add value though, so maybe just
add a blurb in the changelog saying this isn't strictly necessary?
> ctxt->ops->check_pmc(ctxt, rcx))
> return emulate_gp(ctxt, 0);
>
> --
> 2.25.1
>
