Commit 1a7ed1ba authored Jun 21, 2018 by Vlastimil Babka Committed by Thomas Gleixner Jun 21, 2018

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



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: 377eeaa8 ("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>

parent 2207def7

arch/x86/mm/init.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}

Admin message