linux-kernel - Re: [PATCH] KVM: X86: Fix SMRAM accessing even if VM is shutdown

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Date:   Fri, 9 Feb 2018 11:22:44 +0800
From:   Xiao Guangrong <guangrong.xiao@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] KVM: X86: Fix SMRAM accessing even if VM is shutdown



On 02/08/2018 06:31 PM, Paolo Bonzini wrote:
> On 08/02/2018 09:57, Xiao Guangrong wrote:
>>> Maybe it should return RET_PF_EMULATE, which would cause an emulation
>>> failure and then an exit with KVM_EXIT_INTERNAL_ERROR.
>>
>> So the root cause is that a running vCPU accessing the memory whose memslot
>> is being updated (met the condition KVM_MEMSLOT_INVALID is set on the its
>> memslot).
>>
>> The normal #PF handler breaks KVM_RUN and returns -EFAULT to userspace,
>> we'd better to make ept-misconfig's handler follow this style as well.
> 
> Why return -EFAULT and not attempt emulation (which will fail)?
> 

That is a good question... :)

This case (with KVM_MEMSLOT_INVALID is set) can be easily constructed,
userspace should avoid this case by itself (avoiding vCPU accessing the
memslot which is being updated). If it happens, it's a operation issue
rather than INTERNAL ERROR.

Maybe treat it as MMIO accessing and return to userspace with MMIO_EXIT
is a better solution...