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    SubjectRe: [PATCH] Alternate futex non-page-pinning and COW fix
    Linus Torvalds wrote:
    > Actually: the VM_SHARED flag will never change, so testing VM_SHARED is
    > actually the _right_ thing from a mm perspective.

    Yes it can. See sys_mprotect(). If that's not intended, it's a bug
    in mprotect(). What does PROT_SEM mean for Linux, btw?

    See:
    if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
    return -EINVAL;

    and:
    newflags = prot | (vma->vm_flags & ~(PROT_READ | PROT_WRITE | PROT_EXEC));
    if ((newflags & ~(newflags >> 4)) & 0xf) {
    error = -EACCES;
    goto out;
    }

    newflags is than used to index protection_map[], like this:
    newprot = protection_map[newflags & 0xf];

    and that is stored in the page tables.

    -- Jamie
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