Messages in this thread | | | Date | Tue, 3 Apr 2012 16:37:52 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH RFC] mm: account VMA before forced-COW via /proc/pid/mem |
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On 04/02, Konstantin Khlebnikov wrote: > > Currently kernel does not account read-only private mappings into memory commitment. > But these mappings can be force-COW-ed in get_user_pages().
Heh. tail -n3 Documentation/vm/overcommit-accounting may be you should update it then.
Can't really comment the patch, this is not my area. Still,
> + down_write(&mm->mmap_sem); > + *pvma = vma = find_vma(mm, addr); > + if (vma && vma->vm_start <= addr) { > + ret = vma->vm_end - addr; > + if ((vma->vm_flags & (VM_ACCOUNT | VM_NORESERVE | VM_SHARED | > + VM_HUGETLB | VM_MAYWRITE)) == VM_MAYWRITE) { > + if (!security_vm_enough_memory_mm(mm, vma_pages(vma)))
Oooooh, the whole vma. Say, gdb installs the single breakpoint into the huge .text mapping...
I am not sure, but probably you want to check at least VM_IO/PFNMAP as well. We do not want to charge this memory and retry with FOLL_FORCE before vm_ops->access(). Say, /dev/mem.
Hmm. OTOH, if I am right then mprotect_fixup() should be fixed??
We drop ->mmap_sem... Say, the task does mremap() in between and len == 2 * PAGE_SIZE. Then, for example, copy_to_user_page() can write to the same page twice. Perhaps not a problem in practice, I dunno.
Oleg.
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