[PATCH v4 3/5] [RFC] arm64: Add support for idle bit in swap PTE

Joel Fernandes (Google)
2019-08-05T17:05:15Z

This bit will be used by idle page tracking code to correctly identify
if a page that was swapped out was idle before it got swapped out.
Without this PTE bit, we lose information about if a page is idle or not
since the page frame gets unmapped.

In this patch we reuse PTE_DEVMAP bit since idle page tracking only
works on user pages in the LRU. Device pages should not consitute those
so it should be unused and safe to use.

Cc: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/pgtable-prot.h | 1 +
arch/arm64/include/asm/pgtable.h | 15 +++++++++++++++
3 files changed, 17 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3adcec05b1f6..9d1412c693d7 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -128,6 +128,7 @@ config ARM64
select HAVE_ARCH_MMAP_RND_BITS
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
select HAVE_ARCH_PREL32_RELOCATIONS
+ select HAVE_ARCH_PTE_SWP_PGIDLE
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_STACKLEAK
select HAVE_ARCH_THREAD_STRUCT_WHITELIST
diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index 92d2e9f28f28..917b15c5d63a 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -18,6 +18,7 @@
#define PTE_SPECIAL (_AT(pteval_t, 1) << 56)
#define PTE_DEVMAP (_AT(pteval_t, 1) << 57)
#define PTE_PROT_NONE (_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
+#define PTE_SWP_PGIDLE PTE_DEVMAP /* for idle page tracking during swapout */

#ifndef __ASSEMBLY__

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 3f5461f7b560..558f5ebd81ba 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -212,6 +212,21 @@ static inline pte_t pte_mkdevmap(pte_t pte)
return set_pte_bit(pte, __pgprot(PTE_DEVMAP));
}

+static inline int pte_swp_page_idle(pte_t pte)
+{
+ return 0;
+}
+
+static inline pte_t pte_swp_mkpage_idle(pte_t pte)
+{
+ return set_pte_bit(pte, __pgprot(PTE_SWP_PGIDLE));
+}
+
+static inline pte_t pte_swp_clear_page_idle(pte_t pte)
+{
+ return clear_pte_bit(pte, __pgprot(PTE_SWP_PGIDLE));
+}
+
static inline void set_pte(pte_t *ptep, pte_t pte)
{
WRITE_ONCE(*ptep, pte);
--
2.22.0.770.g0f2c4a37fd-goog