Re: [PATCH v5 06/25] mm: Add PG_ARCH_2 page flag

On Wed, Jun 24, 2020 at 07:36:47PM +0100, Matthew Wilcox wrote:

On Wed, Jun 24, 2020 at 11:33:07AM -0700, Andrew Morton wrote:

quoted

On Wed, 24 Jun 2020 18:52:25 +0100 Catalin Marinas [off-list ref] wrote:

quoted

From: Steven Price <steven.price@arm.com>

For arm64 MTE support it is necessary to be able to mark pages that
contain user space visible tags that will need to be saved/restored e.g.
when swapped out.

To support this add a new arch specific flag (PG_ARCH_2) that arch code
can opt into using ARCH_USES_PG_ARCH_2.

...

--- a/fs/proc/page.c
+++ b/fs/proc/page.c

@@ -217,6 +217,9 @@ u64 stable_page_flags(struct page *page)
 	u |= kpf_copy_bit(k, KPF_PRIVATE_2,	PG_private_2);
 	u |= kpf_copy_bit(k, KPF_OWNER_PRIVATE,	PG_owner_priv_1);
 	u |= kpf_copy_bit(k, KPF_ARCH,		PG_arch_1);
+#ifdef CONFIG_ARCH_USES_PG_ARCH_2
+	u |= kpf_copy_bit(k, KPF_ARCH_2,	PG_arch_2);
+#endif

Do we need CONFIG_ARCH_USES_PG_ARCH_2?  What would be the downside to
giving every architecture a PG_arch_2, but only arm64 uses it (at
present)?

32-bit architectures don't have space for it.  We could condition it on
CONFIG_64BIT instead.

I'll this, though we'd still need some #ifdefs (OTOH, we get rid of the
Kconfig entry).

-- 
Catalin

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel