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

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Date:	Wed, 18 Jun 2014 18:29:18 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Nadav Amit <namit@...technion.ac.il>
CC:	gleb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, joro@...tes.org
Subject: Re: [PATCH 2/3] KVM: x86: Emulator support for #UD on CPL>0

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@...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;
>  	}
>
>

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