4.9-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 @@ -175,7 +175,7 @@ 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 @@ -792,7 +792,7 @@ 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 @@ -138,7 +138,7 @@ 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; }