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[PATCH V3 0/3] Numabalancing preserve write fix

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  [PATCH V3 0/3] Numabalancing preserve write fix "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2017-02-19 11:10 +0100
    Re: [PATCH V3 0/3] Numabalancing preserve write fix "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2017-02-19 14:30 +0100

#1584101 — [PATCH V3 0/3] Numabalancing preserve write fix

This patch series address an issue w.r.t THP migration and autonuma
preserve write feature. migrate_misplaced_transhuge_page() cannot deal with
concurrent modification of the page. It does a page copy without
following the migration pte sequence. IIUC, this was done to keep the
migration simpler and at the time of implemenation we didn't had THP
page cache which would have required a more elaborate migration scheme.
That means thp autonuma migration expect the protnone with saved write
to be done such that both kernel and user cannot update
the page content. This patch series enables archs like ppc64 to do that.
We are good with the hash translation mode with the current code,
because we never create a hardware page table entry for a protnone pte. 

Changes form V2:
* Fix kvm crashes due to ksm not clearing savedwrite bit.

Changes from V1:
* Update the patch so that it apply cleanly to upstream.
* Add acked-by from Michael Neuling

Aneesh Kumar K.V (3):
  mm/autonuma: Let architecture override how the write bit should be
    stashed in a protnone pte.
  mm/ksm: Handle protnone saved writes when making page write protect
  powerpc/mm/autonuma: Switch ppc64 to its own implementeation of saved
    write

 arch/powerpc/include/asm/book3s/64/pgtable.h | 52 ++++++++++++++++++++++++----
 include/asm-generic/pgtable.h                | 24 +++++++++++++
 mm/huge_memory.c                             |  6 ++--
 mm/ksm.c                                     |  9 +++--
 mm/memory.c                                  |  2 +-
 mm/mprotect.c                                |  4 +--
 6 files changed, 82 insertions(+), 15 deletions(-)

-- 
2.7.4

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#1584137

I am not sure whether we want to merge this debug patch. This will help
us in identifying wrong pte_wrprotect usage in the kernel.

From a0fbbbbb302fd204159a1327b67decb8f14ffa21 Mon Sep 17 00:00:00 2001
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Date: Sat, 18 Feb 2017 10:39:47 +0530
Subject: [PATCH] powerpc/autonuma: Add debug check for wrong writable pte
 check

With ppc64, protnone ptes don't use _PAGE_WRITE bit for savedwrite. Hence
we need to make sure we don't do pte_write* functions on protnone ptes.
Add debug check to catch wrong usage.

This should be only used for debugging and can give wrong results w.r.t change
bit on radix. Even on hash with kvm we will insert the page table entry in
guest hash page table with write bit set, even if the pte is marked protnone.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h | 130 +++++++++++++++++----------
 1 file changed, 85 insertions(+), 45 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index d87bee85fc44..1c99deac3966 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -341,10 +341,36 @@ static inline int __ptep_test_and_clear_young(struct mm_struct *mm,
 	__r;							\
 })
 
+#undef SAVED_WRITE_DEBUG
+#ifdef CONFIG_NUMA_BALANCING
+static inline int pte_protnone(pte_t pte)
+{
+	/*
+	 * We want to catch wrong usage of pte_write w.r.t protnone ptes.
+	 * The way we do that is to make saved write as _PAGE_WRITE for hash
+	 * translation mode. This only will work with hash translation mode.
+	 */
+#ifdef SAVED_WRITE_DEBUG
+	if (!radix_enabled())
+		return (pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_PRIVILEGED)) ==
+			cpu_to_be64(_PAGE_PRESENT | _PAGE_PRIVILEGED);
+#endif
+	return (pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_PTE | _PAGE_RWX)) ==
+		cpu_to_be64(_PAGE_PRESENT | _PAGE_PTE);
+}
+#endif
+
 #define __HAVE_ARCH_PTEP_SET_WRPROTECT
 static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
 				      pte_t *ptep)
 {
+#ifdef SAVED_WRITE_DEBUG
+	/*
+	 * Cannot use this with protnone pte, For protnone, writes
+	 * will be marked via savedwrite bit.
+	 */
+	VM_WARN_ON(pte_protnone(*ptep));
+#endif
 	if ((pte_raw(*ptep) & cpu_to_be64(_PAGE_WRITE)) == 0)
 		return;
 
@@ -430,51 +456,6 @@ static inline pte_t pte_clear_soft_dirty(pte_t pte)
 }
 #endif /* CONFIG_HAVE_ARCH_SOFT_DIRTY */
 
-#ifdef CONFIG_NUMA_BALANCING
-static inline int pte_protnone(pte_t pte)
-{
-	return (pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_PTE | _PAGE_RWX)) ==
-		cpu_to_be64(_PAGE_PRESENT | _PAGE_PTE);
-}
-
-#define pte_mk_savedwrite pte_mk_savedwrite
-static inline pte_t pte_mk_savedwrite(pte_t pte)
-{
-	/*
-	 * Used by Autonuma subsystem to preserve the write bit
-	 * while marking the pte PROT_NONE. Only allow this
-	 * on PROT_NONE pte
-	 */
-	VM_BUG_ON((pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_RWX | _PAGE_PRIVILEGED)) !=
-		  cpu_to_be64(_PAGE_PRESENT | _PAGE_PRIVILEGED));
-	return __pte(pte_val(pte) & ~_PAGE_PRIVILEGED);
-}
-
-#define pte_clear_savedwrite pte_clear_savedwrite
-static inline pte_t pte_clear_savedwrite(pte_t pte)
-{
-	/*
-	 * Used by KSM subsystem to make a protnone pte readonly.
-	 */
-	VM_BUG_ON(!pte_protnone(pte));
-	return __pte(pte_val(pte) | _PAGE_PRIVILEGED);
-}
-
-#define pte_savedwrite pte_savedwrite
-static inline bool pte_savedwrite(pte_t pte)
-{
-	/*
-	 * Saved write ptes are prot none ptes that doesn't have
-	 * privileged bit sit. We mark prot none as one which has
-	 * present and pviliged bit set and RWX cleared. To mark
-	 * protnone which used to have _PAGE_WRITE set we clear
-	 * the privileged bit.
-	 */
-	VM_BUG_ON(!pte_protnone(pte));
-	return !(pte_raw(pte) & cpu_to_be64(_PAGE_RWX | _PAGE_PRIVILEGED));
-}
-#endif /* CONFIG_NUMA_BALANCING */
-
 static inline int pte_present(pte_t pte)
 {
 	return !!(pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT));
@@ -500,6 +481,14 @@ static inline unsigned long pte_pfn(pte_t pte)
 /* Generic modifiers for PTE bits */
 static inline pte_t pte_wrprotect(pte_t pte)
 {
+
+#ifdef SAVED_WRITE_DEBUG
+	/*
+	 * Cannot use this with protnone pte, For protnone, writes
+	 * will be marked via savedwrite bit.
+	 */
+	VM_WARN_ON(pte_protnone(pte));
+#endif
 	return __pte(pte_val(pte) & ~_PAGE_WRITE);
 }
 
@@ -552,6 +541,57 @@ static inline bool pte_user(pte_t pte)
 	return !(pte_raw(pte) & cpu_to_be64(_PAGE_PRIVILEGED));
 }
 
+#ifdef CONFIG_NUMA_BALANCING
+#define pte_mk_savedwrite pte_mk_savedwrite
+static inline pte_t pte_mk_savedwrite(pte_t pte)
+{
+#ifdef SAVED_WRITE_DEBUG
+	if (!radix_enabled())
+		return pte_mkwrite(pte);
+#endif
+	/*
+	 * Used by Autonuma subsystem to preserve the write bit
+	 * while marking the pte PROT_NONE. Only allow this
+	 * on PROT_NONE pte
+	 */
+	VM_BUG_ON((pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_RWX | _PAGE_PRIVILEGED)) !=
+		  cpu_to_be64(_PAGE_PRESENT | _PAGE_PRIVILEGED));
+	return __pte(pte_val(pte) & ~_PAGE_PRIVILEGED);
+}
+
+#define pte_clear_savedwrite pte_clear_savedwrite
+static inline pte_t pte_clear_savedwrite(pte_t pte)
+{
+	/*
+	 * Used by KSM subsystem to make a protnone pte readonly.
+	 */
+	VM_BUG_ON(!pte_protnone(pte));
+#ifdef SAVED_WRITE_DEBUG
+	if (!radix_enabled())
+		return __pte(pte_val(pte) & ~_PAGE_WRITE);
+#endif
+	return __pte(pte_val(pte) | _PAGE_PRIVILEGED);
+}
+
+#define pte_savedwrite pte_savedwrite
+static inline bool pte_savedwrite(pte_t pte)
+{
+	/*
+	 * Saved write ptes are prot none ptes that doesn't have
+	 * privileged bit sit. We mark prot none as one which has
+	 * present and pviliged bit set and RWX cleared. To mark
+	 * protnone which used to have _PAGE_WRITE set we clear
+	 * the privileged bit.
+	 */
+	VM_BUG_ON(!pte_protnone(pte));
+#ifdef SAVED_WRITE_DEBUG
+	if (!radix_enabled())
+		return pte_write(pte);
+#endif
+	return !(pte_raw(pte) & cpu_to_be64(_PAGE_RWX | _PAGE_PRIVILEGED));
+}
+#endif /* CONFIG_NUMA_BALANCING */
+
 /* Encode and de-code a swap entry */
 #define MAX_SWAPFILES_CHECK() do { \
 	BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > SWP_TYPE_BITS); \
-- 
2.7.4

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