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SubjectRe: [crash] Re: Latest brk patchset
H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
>> Yinghai Lu wrote:
>>>> -INIT_MAP_SIZE = (PAGE_TABLE_SIZE + ALLOCATOR_SLOP) * PAGE_SIZE_asm
>>>> -RESERVE_BRK(pagetables, INIT_MAP_SIZE)
>>>> +/* Enough space to fit pagetables for the low memory linear map */
>>>> +MAPPING_BEYOND_END = (PAGE_TABLE_SIZE(1 << (32 - PAGE_SHIFT)) *
>>>> PAGE_SIZE)
>>>>
>>>
>>> that is for 4g?
>>>
>>
>> Yes, I suppose it only needs to be 1G. But it doesn't make much
>> difference in practice.
>>
>
> A tighter bound would probably be nice, if nothing else because
> tighter bounds tend to catch more bugs.

Well, its a bit more complex than that; we'd need to make it conditional
on the user/kernel split, which seems all a bit fiddly. I guess it
could be something like:

MAPPING_BEYOND_END = PAGE_TABLE_SIZE((1<<(32-PAGE_SHIFT)) - (PAGE_OFFSET / PAGE_SIZE)) * PAGE_SIZE

J


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