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

[Jan Kiszka]

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).

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.

Jan

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