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x86/speculation/l1tf: Extend 64bit swap file size limit

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The previous patch has limited swap file size so that large offsets cannot
clear bits above MAX_PA/2 in the pte and interfere with L1TF mitigation.

It assumed that offsets are encoded starting with bit 12, same as pfn. But
on x86_64, offsets are encoded starting with bit 9.

Thus the limit can be raised by 3 bits. That means 16TB with 42bit MAX_PA
and 256TB with 46bit MAX_PA.

Fixes: 377eeaa8e1 ("x86/speculation/l1tf: Limit swap file size to MAX_PA/2")
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Vlastimil Babka 2018-06-21 12:36:29 +02:00 committed by Thomas Gleixner
parent 2207def700
commit 1a7ed1ba4b
1 changed files with 9 additions and 1 deletions
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10
arch/x86/mm/init.c
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@ -891,7 +891,15 @@ 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 */
pages = min_t(unsigned long, l1tf_pfn_limit() + 1, pages);
unsigned 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.
*/
#ifdef CONFIG_X86_64
l1tf_limit <<= PAGE_SHIFT - SWP_OFFSET_FIRST_BIT;
#endif
pages = min_t(unsigned long, l1tf_limit, pages);
}
return pages;
}