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    Subject[PATCH 4.18 052/123] x86/speculation/l1tf: Fix off-by-one error when warning that system has too much RAM
    Date
    4.18-stable review patch.  If anyone has any objections, please let me know.

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

    From: Vlastimil Babka <vbabka@suse.cz>

    commit b0a182f875689647b014bc01d36b340217792852 upstream.

    Two users have reported [1] that they have an "extremely unlikely" system
    with more than MAX_PA/2 memory and L1TF mitigation is not effective. In
    fact it's a CPU with 36bits phys limit (64GB) and 32GB memory, but due to
    holes in the e820 map, the main region is almost 500MB over the 32GB limit:

    [ 0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000081effffff] usable

    Suggestions to use 'mem=32G' to enable the L1TF mitigation while losing the
    500MB revealed, that there's an off-by-one error in the check in
    l1tf_select_mitigation().

    l1tf_pfn_limit() returns the last usable pfn (inclusive) and the range
    check in the mitigation path does not take this into account.

    Instead of amending the range check, make l1tf_pfn_limit() return the first
    PFN which is over the limit which is less error prone. Adjust the other
    users accordingly.

    [1] https://bugzilla.suse.com/show_bug.cgi?id=1105536

    Fixes: 17dbca119312 ("x86/speculation/l1tf: Add sysfs reporting for l1tf")
    Reported-by: George Anchev <studio@anchev.net>
    Reported-by: Christopher Snowhill <kode54@gmail.com>
    Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: "H . Peter Anvin" <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/20180823134418.17008-1-vbabka@suse.cz
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/include/asm/processor.h | 2 +-
    arch/x86/mm/init.c | 2 +-
    arch/x86/mm/mmap.c | 2 +-
    3 files changed, 3 insertions(+), 3 deletions(-)

    --- a/arch/x86/include/asm/processor.h
    +++ b/arch/x86/include/asm/processor.h
    @@ -183,7 +183,7 @@ extern void cpu_detect(struct cpuinfo_x8

    static inline unsigned long long l1tf_pfn_limit(void)
    {
    - return BIT_ULL(boot_cpu_data.x86_phys_bits - 1 - PAGE_SHIFT) - 1;
    + return BIT_ULL(boot_cpu_data.x86_phys_bits - 1 - PAGE_SHIFT);
    }

    extern void early_cpu_init(void);
    --- a/arch/x86/mm/init.c
    +++ b/arch/x86/mm/init.c
    @@ -923,7 +923,7 @@ 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 */
    - unsigned long long l1tf_limit = l1tf_pfn_limit() + 1;
    + unsigned long long l1tf_limit = l1tf_pfn_limit();
    /*
    * We encode swap offsets also with 3 bits below those for pfn
    * which makes the usable limit higher.
    --- a/arch/x86/mm/mmap.c
    +++ b/arch/x86/mm/mmap.c
    @@ -257,7 +257,7 @@ bool pfn_modify_allowed(unsigned long pf
    /* If it's real memory always allow */
    if (pfn_valid(pfn))
    return true;
    - if (pfn > l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN))
    + if (pfn >= l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN))
    return false;
    return true;
    }

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