linux-kernel - Re: [PATCH 1/2] KVM: Exception during emulation decode should propagate

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Date:	Thu, 12 Jan 2012 07:11:37 +0900
From:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
To:	Nadav Amit <namit@...technion.ac.il>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Nadav Amit <nadav.amit@...il.com>
Subject: Re: [PATCH 1/2] KVM: Exception during emulation decode should
 propagate

On Wed, 11 Jan 2012 18:53:30 +0200
Nadav Amit <namit@...technion.ac.il> wrote:

> An exception might occur during decode (e.g., #PF during fetch).
> Currently, the exception is ignored and emulation is performed.

When I cleaned up insn_fetch(), I thought that fetching the instruction
which is being executed by the guest cannot cause #PF.

The possibility that a meaningless userspace might similtaneously unmap
the page, noted by Avi IIRC, was ignored intentionally, so we just fail
in such a case.

Did you see any real problem?

	Takuya


> Instead, emulation should be skipped and the fault should be injected.
> Skipping instruction should report a failure in this case.
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