Re: [PATCH 2/3] KVM: x86: Emulator support for #UD on CPL>0

Paolo Bonzini
2014-06-18T16:29:41Z

Il 18/06/2014 16:19, Nadav Amit ha scritto:
> Certain instructions (e.g., mwait and monitor) cause a #UD exception when they
> are executed in privilaged mode.

It's actually "non-privileged mode" (Priv means the instruction is
privileged, not the mode). So I've renamed the flag to PrivUD.

Paolo

This is in contrast to the regular privilaged
> instructions which cause #GP. In order not to mess with SVM interception of
> mwait and monitor which assumes privilage level assertions take place before
> interception, a flag has been added.
>
> Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
> ---
> arch/x86/kvm/emulate.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index f90194d..ef7a5a0 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -163,6 +163,7 @@
> #define SrcWrite ((u64)1 << 46) /* Write back src operand */
> #define NoMod ((u64)1 << 47) /* Mod field is ignored */
> #define NoBigReal ((u64)1 << 48) /* No big real mode */
> +#define UDOnPriv ((u64)1 << 49) /* #UD instead of #GP on CPL > 0 */
>
> #define DstXacc (DstAccLo | SrcAccHi | SrcWrite)
>
> @@ -4560,7 +4561,10 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
>
> /* Privileged instruction can be executed only in CPL=0 */
> if ((ctxt->d & Priv) && ops->cpl(ctxt)) {
> - rc = emulate_gp(ctxt, 0);
> + if (ctxt->d & UDOnPriv)
> + rc = emulate_ud(ctxt);
> + else
> + rc = emulate_gp(ctxt, 0);
> goto done;
> }
>
>