Re: [Qemu-devel] [PATCH] TCG: Fix TB invalidation after breakpoint insertion/deletion

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-05-24 11:29, Max Filippov wrote:
> On Thu, May 24, 2012 at 6:21 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>> On 2012-05-24 11:11, Max Filippov wrote:
>>> On Thu, May 24, 2012 at 5:26 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>>>> On 2012-05-24 09:42, Max Filippov wrote:
>>>>> On Thu, May 24, 2012 at 4:16 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>>>>>> On 2012-05-24 09:08, Max Filippov wrote:
>>>>>>> On Thu, May 24, 2012 at 3:25 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>>>>>>>> On 2012-05-24 07:51, Max Filippov wrote:
>>>>>>>>> On Thu, May 24, 2012 at 6:34 AM, Jan Kiszka <jan.kiszka@web.de> wrote:
>>>>>>>>>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>>>>>>>>>
>>>>>>>>>> tb_invalidate_phys_addr has to called with the exact physical address of
>>>>>>>>>> the breakpoint we add/remove, not just the page's base address.
>>>>>>>>>> Otherwise we easily fail to flush the right TB.
>>>>>>>>>>
>>>>>>>>>> Regression of 1e7855a558.
>>>>>>>>>
>>>>>>>>> Sorry, I fail to see how 1e7855a558 could introduce a regression, it
>>>>>>>>> just rearranged the code.
>>>>>>>>> Even more, AFAIK cpu_get_phys_page_debug returns complete physical
>>>>>>>>> address, not just
>>>>>>>>> physical page. Probably it has a misleading name.
>>>>>>>>
>>>>>>>> Unfortunately, cpu_get_phys_page_debug does NOT deliver the sub-page
>>>>>>>> offset, only the page base address.
>>>>>>>
>>>>>>> Ok, i386 has probably the most explicit implementation,
>>>>>>> let's look at the target-i386/helper.c:876
>>>>>>>
>>>>>>>     page_offset = (addr & TARGET_PAGE_MASK) & (page_size - 1);
>>>>>>>     paddr = (pte & TARGET_PAGE_MASK) + page_offset;
>>>>>>>     return paddr;
>>>>>>>
>>>>>>> that's clearly physical page plus in-page offset.
>>>>>>> I can provide other samples (:
>>>>>>
>>>>>> "page_offset" is misleading: addr & TARGET_PAGE_MASK kills all the
>>>>>> offset bits. It will only contain the relevant bits between page_size
>>>>>> and TARGET_PAGE_SIZE.
>>>>>>
>>>>>> Check also ppc's cpu_get_phys_page_debug, it's clearer in this regard.
>>>>>
>>>>> Ok, for i386, ppc, microblaze (and maybe others) you're right.
>>>>> What about ARM, CRIS, MIPS, SH4, xtensa (and maybe others)?
>>>>> Looks like this is a long-standing discrepancy and consequently
>>>>> a long-standing bug in the breakpoint_invalidate.
>>>>
>>>> Not in breakpoint_invalidate as the missing offset was compensated
>>>> before your commit (well, starting with c2f07f81a2 in fact).
>>>
>>> I'd say that compensation that you mention
>>>
>>>     ram_addr = (memory_region_get_ram_addr(section.mr)
>>>                 + section.offset_within_region) & TARGET_PAGE_MASK;
>>> this >>>>    ram_addr |= (pc & ~TARGET_PAGE_MASK);
>>>     tb_invalidate_phys_page_range(ram_addr, ram_addr + 1, 0);
>>>
>>> was removed by f3705d53296d, not by 1e7855a558
>>
>> Unless I misinterpret section_addr, it does return the lower address
>> bits unmodified.
> 
> Maybe, but
> 
> addr = cpu_get_phys_page_debug(env, pc);
> 
> which should have lost its in-page offset according to you.

Err, right.

Jan

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