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    SubjectRe: [PATCH RFC] mm: account VMA before forced-COW via /proc/pid/mem
    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 |
    > + 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.


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