[PATCH 3.16 112/131] x86/speculation/l1tf: Fix overflow in l1tf_pfn_limit() on 32bit

[Ben Hutchings]

3.16.59-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Vlastimil Babka <vbabka@xxxxxxx>

commit 9df9516940a61d29aedf4d91b483ca6597e7d480 upstream.

On 32bit PAE kernels on 64bit hardware with enough physical bits,
l1tf_pfn_limit() will overflow unsigned long. This in turn affects
max_swapfile_size() and can lead to swapon returning -EINVAL. This has been
observed in a 32bit guest with 42 bits physical address size, where
max_swapfile_size() overflows exactly to 1 << 32, thus zero, and produces
the following warning to dmesg:

[    6.396845] Truncating oversized swap area, only using 0k out of 2047996k

Fix this by using unsigned long long instead.

Fixes: 17dbca119312 ("x86/speculation/l1tf: Add sysfs reporting for l1tf")
Fixes: 377eeaa8e11f ("x86/speculation/l1tf: Limit swap file size to MAX_PA/2")
Reported-by: Dominique Leuenberger <dimstar@xxxxxxx>
Reported-by: Adrian Schroeter <adrian@xxxxxxx>
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20180820095835.5298-1-vbabka@xxxxxxx
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/processor.h | 4 ++--
 arch/x86/mm/init.c               | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -165,9 +165,9 @@ extern const struct seq_operations cpuin
 extern void cpu_detect(struct cpuinfo_x86 *c);
 extern void fpu_detect(struct cpuinfo_x86 *c);
 
-static inline unsigned long l1tf_pfn_limit(void)
+static inline unsigned long long l1tf_pfn_limit(void)
 {
-	return BIT(boot_cpu_data.x86_phys_bits - 1 - PAGE_SHIFT) - 1;
+	return BIT_ULL(boot_cpu_data.x86_phys_bits - 1 - PAGE_SHIFT) - 1;
 }
 
 extern void early_cpu_init(void);
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -710,7 +710,7 @@ 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 l1tf_limit = l1tf_pfn_limit() + 1;
+		unsigned long 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.
@@ -718,7 +718,7 @@ unsigned long max_swapfile_size(void)
 #if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
 		l1tf_limit <<= PAGE_SHIFT - SWP_OFFSET_FIRST_BIT;
 #endif
-		pages = min_t(unsigned long, l1tf_limit, pages);
+		pages = min_t(unsigned long long, l1tf_limit, pages);
 	}
 	return pages;
 }