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    SubjectRe: [PATCHv3 33/33] mm, x86: introduce PR_SET_MAX_VADDR and PR_GET_MAX_VADDR
    On Fri, Feb 17, 2017 at 9:19 AM, Dave Hansen <dave.hansen@intel.com> wrote:
    > On 02/17/2017 06:13 AM, Kirill A. Shutemov wrote:
    >> +/*
    >> + * Default maximum virtual address. This is required for
    >> + * compatibility with applications that assumes 47-bit VA.
    >> + * The limit can be changed with prctl(PR_SET_MAX_VADDR).
    >> + */
    >> +#define MAX_VADDR_DEFAULT ((1UL << 47) - PAGE_SIZE)
    >
    > This is a bit goofy. It's not the largest virtual adddress that can be
    > accessed, but the beginning of the last page.

    No, it really is the limit. We don't allow user code to map the last
    page because ti would be a root hole due to SYSRET. Thanks, Intel.
    See the comment near TASK_SIZE_MAX IIRC.

    --Andy

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