linux-kernel - Re: [PATCH] KVM: x86: emulate: correct page fault error code for NoWrite instructions

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Message-Id: <934F9FF2-D571-485C-9117-CC6B6F617C32@gmail.com>
Date:	Tue, 10 Feb 2015 19:56:10 -0500
From:	Nadav Amit <nadav.amit@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Nadav Amit <namit@...technion.ac.il>
Subject: Re: [PATCH] KVM: x86: emulate: correct page fault error code for NoWrite instructions

Sorry for that. I’ll try to run some few more tests next week.

Nadav

Paolo Bonzini <pbonzini@...hat.com> wrote:

> NoWrite instructions (e.g. cmp or test) never set the "write access"
> bit in the error code, even if one of the operands is treated as a
> destination.
> 
> Fixes: c205fb7d7d4f81e46fc577b707ceb9e356af1456
> Cc: Nadav Amit <namit@...technion.ac.il>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
> 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 81dcf7964701..a943bf0c06d0 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -4954,7 +4954,8 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
> 		rc = segmented_read(ctxt, ctxt->dst.addr.mem,
> 				   &ctxt->dst.val, ctxt->dst.bytes);
> 		if (rc != X86EMUL_CONTINUE) {
> -			if (rc == X86EMUL_PROPAGATE_FAULT &&
> +			if (!(ctxt->d & NoWrite) &&
> +			    rc == X86EMUL_PROPAGATE_FAULT &&
> 			    ctxt->exception.vector == PF_VECTOR)
> 				ctxt->exception.error_code |= PFERR_WRITE_MASK;
> 			goto done;
> -- 
> 1.8.3.1
> 
> --
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