Re: [Qemu-devel] [PATCH] exec: Handle multipage ranges in invalidate_and_set_dirty()

[Peter Maydell]

On 17 November 2014 11:03, Paolo Bonzini <address@hidden> wrote:
>
>
> On 16/11/2014 20:44, Peter Maydell wrote:
>> The code in invalidate_and_set_dirty() needs to handle addr/length
>> combinations which cross guest physical page boundaries. This can happen,
>> for example, when disk I/O reads large blocks into guest RAM which previously
>> held code that we have cached translations for. Unfortunately we were only
>> checking the clean/dirty status of the first page in the range, and then
>> were calling a tb_invalidate function which only handles ranges that don't
>> cross page boundaries. Fix the function to deal with multipage ranges.
>>
>> The symptoms of this bug were that guest code would misbehave (eg segfault),
>> in particular after a guest reboot but potentially any time the guest
>> reused a page of its physical RAM for new code.
>>
>> Cc: address@hidden
>> Signed-off-by: Peter Maydell <address@hidden>
>> ---
>> This seems pretty nasty, and I have no idea why it hasn't been wreaking
>> more havoc than this before. I'm not entirely sure why we invalidate TBs
>> if any of the dirty bits is set rather than only if the code bit is set,
>> but I left that logic as it is.
>
> I think it's a remain of when we had a single bitmap with three bits in
> it.  We can clean up in 2.3.
>
>> Review appreciated -- it would be nice to get this into rc2 if
>> we can, I think.
>
> Reviewed-by: Paolo Bonzini <address@hidden>

Applied to master; thanks.

-- PMM