Re: [Qemu-devel] [PATCH for-2.0?] target-i386: fix gdb debugging with large memory guests

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

On 2014-03-18 17:37, Paolo Bonzini wrote:
> Il 18/03/2014 17:23, Luiz Capitulino ha scritto:
>> On Tue, 18 Mar 2014 15:36:45 +0100
>> Jan Kiszka <jan.kiszka@siemens.com> wrote:
>>
>>>>> Right, this belongs in the "if (env->hflags & HF_LMA_MASK)" block.
>>>>>
>>>>> And the subject or description should mention that
>>>>> x86_cpu_get_phys_page_debug was lacking support for 1G hugepages.
>>>>
>>>> To be honest, although the PS bit is set and that indicates a 1GB page,
>>>> I didn't know Linux does that. I thought Linux would use 4KB pages for
>>>> everything unless it's explicitly asked to use bigger pages. Also,
>>>> note that
>>>> I was using gdb to debug really early kernel boot code
>>>> (start_kernel()).
>>>
>>> I could imagine that Linux initially creates a giant identity mapping
>>> page table for the startup process and only later on switches to
>>> fine-grained tables of 4K and 2M pages. Giant pages still require
>>> hughtlbfs, IIRC.
>>>
>>>>
>>>> I'd feel more confident to have such a changelog after I find out where
>>>> exactly Linux sets that bit, but I won't have time in the next days.
>>>> On the
>>>> other hand, the patch does fix the problem to me.
>>>
>>> Don't worry about Linux (the code should work with any OS anyway), just
>>> believe your reviewers. ;) Alternatively, check Intel IA32 SDM on page
>>> table structures.
>>
>> OK, so you want me to change the subject? Anything else for v2?
> 
> You only need to move the new code into the "if (env->hflags &
> HF_LMA_MASK)", I think.  The subject is ok.

Yes. Subject is fine, a reference to GB pages in the description would
be nice-to-have.

Jan

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