Messages in this thread | | | Subject | Re: [PATCHv2 3/5] x86/mm: fix native mmap() in compat bins and vice-versa | From | Dmitry Safonov <> | Date | Wed, 18 Jan 2017 14:33:26 +0300 |
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On 01/17/2017 11:29 PM, Andy Lutomirski wrote: > On Mon, Jan 16, 2017 at 4:33 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote: >> Fix 32-bit compat_sys_mmap() mapping VMA over 4Gb in 64-bit binaries >> and 64-bit sys_mmap() mapping VMA only under 4Gb in 32-bit binaries. >> Changed arch_get_unmapped_area{,_topdown}() to recompute mmap_base >> for those cases and use according high/low limits for vm_unmapped_area() >> The recomputing of mmap_base may make compat sys_mmap() in 64-bit >> binaries a little slower than native, which uses already known from exec >> time mmap_base - but, as it returned buggy address, that case seemed >> unused previously, so no performance degradation for already used ABI. > > This looks plausibly correct but rather weird -- why does this code > need to distinguish between all four cases (pure 32-bit, pure 64-bit, > 64-bit mmap layout doing 32-bit call, 32-bit layout doing 64-bit > call)?
Only by need to know is mm->mmap_base computed initialy for 32-bit or for 64-bit.
> >> Can be optimized in future by introducing mmap_compat_{,legacy}_base >> in mm_struct. > > Hmm. Would it make sense to do it this way from the beginning?
That would, but mm_struct is in generic code, if adding those new bases is fine, than I'll do that in v3.
It will look somehow like: : if (in_compat_syscall()) : return current->mm->mmap_compat_base; : else : return current->mm->mmap_base;
> > If adding an in_32bit_syscall() helper would help, then by all means > please do so. > > --Andy >
-- Dmitry
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