From b0a182f875689647b014bc01d36b340217792852 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Thu, 23 Aug 2018 15:44:18 +0200
Subject: [PATCH] x86/speculation/l1tf: Fix off-by-one error when warning that
system has too much RAM
Git-commit: b0a182f875689647b014bc01d36b340217792852
Patch-mainline: v4.19-rc1
References: bnc#1105536
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
Acked-by: Michal Hocko <mhocko@suse.com>
---
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
@@ -184,7 +184,7 @@ 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
@@ -893,7 +893,7 @@ 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
@@ -189,7 +189,7 @@ 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;
}