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

[Max Filippov]

On Thu, May 24, 2012 at 6:21 PM, Jan Kiszka <address@hidden> wrote:
> On 2012-05-24 11:11, Max Filippov wrote:
>> On Thu, May 24, 2012 at 5:26 PM, Jan Kiszka <address@hidden> wrote:
>>> On 2012-05-24 09:42, Max Filippov wrote:
>>>> On Thu, May 24, 2012 at 4:16 PM, Jan Kiszka <address@hidden> wrote:
>>>>> On 2012-05-24 09:08, Max Filippov wrote:
>>>>>> On Thu, May 24, 2012 at 3:25 PM, Jan Kiszka <address@hidden> wrote:
>>>>>>> On 2012-05-24 07:51, Max Filippov wrote:
>>>>>>>> On Thu, May 24, 2012 at 6:34 AM, Jan Kiszka <address@hidden> wrote:
>>>>>>>>> From: Jan Kiszka <address@hidden>
>>>>>>>>>
>>>>>>>>> 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.

>>
>>> But it looks like cpu_get_phys_page_debug was broken for quite a while.
>>> Let's fix those archs to return more than page-aligned addresses.
>>
>> You mean make them all return full physical address?
>> I'd propose to rename the function then as well.
>
> No, to return the page base address like x86 etc. do and like most if
> not all users expect it to. So fix ARM & Co.

-- 
Thanks.
-- Max