[PATCH v5 4/6] [RFC] arm64: Add support for idle bit in swap PTE

From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To: linux-kernel@vger.kernel.org
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>,
	Brendan Gregg <bgregg@netflix.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christian Hansen <chansen3@cisco.com>,
	dancol@google.com, fmayer@google.com,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	joelaf@google.com, Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	kernel-team@android.com, linux-api@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, Michal Hocko <mhocko@suse.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	minchan@kernel.org, namhyung@google.com, paulmck@linux.ibm.com,
	Roman Gushchin <guro@fb.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	surenb@google.com, Thomas Gleixner <tglx@linutronix.de>,
	tkjos@google.com, Vladimir Davydov <vdavydov.dev@gmail.com>,
	Vlastimil Babka <vbabka@suse.cz>, Will Deacon <will@kernel.org>
Subject: [PATCH v5 4/6] [RFC] arm64: Add support for idle bit in swap PTE
Date: Wed,  7 Aug 2019 13:15:57 -0400	[thread overview]
Message-ID: <20190807171559.182301-4-joel@joelfernandes.org> (raw)
In-Reply-To: <20190807171559.182301-1-joel@joelfernandes.org>

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

