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Re: [Qemu-devel] [PATCH] exec: fix breakpoint_invalidate() breakage


From: TeLeMan
Subject: Re: [Qemu-devel] [PATCH] exec: fix breakpoint_invalidate() breakage
Date: Thu, 24 May 2012 09:29:06 +0800

On Thu, May 24, 2012 at 1:36 AM, Jan Kiszka <address@hidden> wrote:
> On 2012-05-23 13:02, Jan Kiszka wrote:
>> On 2012-05-23 11:11, TeLeMan wrote:
>>> On Wed, May 23, 2012 at 7:22 PM, Jan Kiszka <address@hidden> wrote:
>>>> On 2012-05-23 04:09, TeLeMan wrote:
>>>>> On Wed, May 23, 2012 at 11:41 AM, Andreas Färber <address@hidden> wrote:
>>>>>> Am 18.05.2012 11:49, schrieb TeLeMan:
>>>>>>> This breakage was introduced by the commit "memory: make
>>>>>>> phys_page_find() return an unadjusted".
>>>>>>
>>>>>> You seem to have found the origin of your problem. If you also mention
>>>>>> the commit hash in your commit message then certain frontends (gitk,
>>>>>> repo.or.cz) will display it as a handy hyperlink to that commit.
>>>>>>
>>>>>>>
>>>>>>> Signed-off-by: TeLeMan <address@hidden>
>>>>>>
>>>>>> Signed-off-by is a legal statement of origin and must not be a pseudonym.
>>>>> Ok, please ignore this patch. I won't submit any patch just report bugs.
>>>>
>>>> Then please describe this bug in more details, e.g. how to reproduce.
>>> I think its evident. cpu_get_phys_page_debug(env, pc) is not the
>>> physical address of pc but the physical page base address of pc.
>>
>> ...so this bites us if the instruction spans two pages as
>> tb_invalidate_phys_addr requests invalidation on a page granularity.
>
> In fact, this is irrelevant. We only need to flush the address at which
> the instruction starts, and that is achieved by flushing all TB that
> relate to that page as the current code does.

But the instruction start is wrong and its TB may not be found. For example,
the pc is 0x1234 and its physical address is 0x1234. The correct
"start" and "end" of tb_invalidate_phys_page_range() is 0x1234 and
0x1235. But now the "start" and "end" is 0x1000 and 0x1001.
If 0x1000 is not translated yet, the real TB won't be invalidated.

> So, again my question: How can I reproduce the issue you see?
>
> Jan
>
> --
> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux



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