Subject: Re: [PATCH 06/10] KVM: x86: MMU: Consolidate WARN_ON/BUG_ON checks
 for reverse-mapped sptes
To: Marcelo Tosatti <mtosatti@redhat.com>
References: <20151112204849.ba920599a8426d7196a0df73@lab.ntt.co.jp>
 <20151112205343.61fbcc0a911e891b1ddc8f19@lab.ntt.co.jp>
 <20151113220819.GA30105@amt.cnet>
Cc: pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org
From: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Message-ID: <56494ED3.20301@lab.ntt.co.jp>
Date: Mon, 16 Nov 2015 12:34:43 +0900
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On 2015/11/14 7:08, Marcelo Tosatti wrote:
> On Thu, Nov 12, 2015 at 08:53:43PM +0900, Takuya Yoshikawa wrote:
>> At some call sites of rmap_get_first() and rmap_get_next(), BUG_ON is
>> placed right after the call to detect unrelated sptes which must not be
>> found in the reverse-mapping list.
>>
>> Move this check in rmap_get_first/next() so that all call sites, not
>> just the users of the for_each_rmap_spte() macro, will be checked the
>> same way.  In addition, change the BUG_ON to WARN_ON since killing the
>> whole host is the last thing that KVM should try.
>
> It should be a BUG_ON, if KVM continues it will corrupt (more) memory.

In the sense that we cannot predict what kind of corruption it will
cause, I agree with you.

But if it can only corrupt that guest's memory, it is a bit sad to
kill unrelated guests, and host, too.  Anyway, since we cannot say
for sure what a possible bug can cause, I agree with you now.

Thanks,
   Takuya

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