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    Subject[PATCH 4.18 28/79] x86/speculation/l1tf: Extend 64bit swap file size limit
    Date
    4.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Vlastimil Babka <vbabka@suse.cz>

    The previous patch has limited swap file size so that large offsets cannot
    clear bits above MAX_PA/2 in the pte and interfere with L1TF mitigation.

    It assumed that offsets are encoded starting with bit 12, same as pfn. But
    on x86_64, offsets are encoded starting with bit 9.

    Thus the limit can be raised by 3 bits. That means 16TB with 42bit MAX_PA
    and 256TB with 46bit MAX_PA.

    Fixes: 377eeaa8e11f ("x86/speculation/l1tf: Limit swap file size to MAX_PA/2")
    Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/mm/init.c | 10 +++++++++-
    1 file changed, 9 insertions(+), 1 deletion(-)

    --- a/arch/x86/mm/init.c
    +++ b/arch/x86/mm/init.c
    @@ -891,7 +891,15 @@ unsigned long max_swapfile_size(void)

    if (boot_cpu_has_bug(X86_BUG_L1TF)) {
    /* Limit the swap file size to MAX_PA/2 for L1TF workaround */
    - pages = min_t(unsigned long, l1tf_pfn_limit() + 1, pages);
    + unsigned long l1tf_limit = l1tf_pfn_limit() + 1;
    + /*
    + * We encode swap offsets also with 3 bits below those for pfn
    + * which makes the usable limit higher.
    + */
    +#ifdef CONFIG_X86_64
    + l1tf_limit <<= PAGE_SHIFT - SWP_OFFSET_FIRST_BIT;
    +#endif
    + pages = min_t(unsigned long, l1tf_limit, pages);
    }
    return pages;
    }

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