From b0a182f875689647b014bc01d36b340217792852 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Thu, 23 Aug 2018 15:44:18 +0200 Subject: x86/speculation/l1tf: Fix off-by-one error when warning that system has too much RAM 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 Reported-by: Christopher Snowhill Signed-off-by: Vlastimil Babka Signed-off-by: Thomas Gleixner Cc: "H . Peter Anvin" Cc: Linus Torvalds Cc: Andi Kleen Cc: Dave Hansen Cc: Michal Hocko Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20180823134418.17008-1-vbabka@suse.cz --- arch/x86/mm/init.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/mm/init.c') diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index 02de3d6065c4..63a6f9fcaf20 100644 --- 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. -- cgit v1.2.3