linux-kernel - Re: [PATCH v2 0/5] KVM: x86: improve reexecute

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Message-ID: <20121213225408.GB11385@amt.cnet>
Date:	Thu, 13 Dec 2012 20:54:08 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Gleb Natapov <gleb@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 0/5] KVM: x86: improve reexecute_instruction

On Thu, Dec 13, 2012 at 04:05:55AM +0800, Xiao Guangrong wrote:
> On 12/12/2012 07:36 AM, Marcelo Tosatti wrote:
> > On Mon, Dec 10, 2012 at 05:11:35PM +0800, Xiao Guangrong wrote:
> >> Changelog:
> >> There are some changes from Marcelo and Gleb's review, thank you all!
> >> - access indirect_shadow_pages in the protection of mmu-lock
> >> - fix the issue when unhandleable instruction access on large page
> >> - add a new test case for large page
> >>
> >> The current reexecute_instruction can not well detect the failed instruction
> >> emulation. It allows guest to retry all the instructions except it accesses
> >> on error pfn.
> >>
> >> For example, these cases can not be detected:
> >> - for tdp used
> >>   currently, it refused to retry all instructions. If nested npt is used, the
> >>   emulation may be caused by shadow page, it can be fixed by unshadow the
> >>   shadow page.
> >>
> >> - for shadow mmu
> >>   some cases are nested-write-protect, for example, if the page we want to
> >>   write is used as PDE but it chains to itself. Under this case, we should
> >>   stop the emulation and report the case to userspace.
> >>
> >> There are two test cases based on kvm-unit-test can trigger a infinite loop on
> >> current code (ept = 0), after this patchset, it can report the error to Qemu.
> >>
> >> Subject: [PATCH] access test: test unhandleable instruction
> >>
> >> Test the instruction which can not be handled by kvm
> >>
> >> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> > 
> > Please submit the test for inclusion. There should be some way to make
> > it fail.. 
> 
> Yes.
> 
> But it is not easy. If the test cases run normally, kvm will report a error to Qemu
> then Qemu will exit the vcpu thread after dumping the vcpu state.
> 
> We need to do something to let guest can be aware that the error report is triggered.
> I guess we can add a option in Qemu, say '-notify-guest' and allow Qemu to inject #GP
> to guest with a special ERROR_CODE if error is reported.
> 
> > program a timer interrupt and #GP? 
> 
> Could you please explain the detail?

Before the instruction which writes continuously to the pagetable, arm
say lapic timer. #GP on the interrupt handler and test with failure.

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