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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 0/9] arm64: Enable contiguous pte hugepage support
Date: Thu, 10 Aug 2017 18:08:57 +0100
Message-Id: <20170810170906.30772-1-punit.agrawal@arm.com>
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To: will.deacon@arm.com, catalin.marinas@arm.com
Cc: Punit Agrawal <punit.agrawal@arm.com>, linux-mm@kvack.org, steve.capper@arm.com, linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com

Hi,

This series re-enables contiguous hugepage support for arm64. In v6,
I've addressed all the concerns raised on the previous version.

Notable changes in this version -

* Patch 4 - "Add break-before-make logic for contiguous entries"
  - added clear_flush() and use it in set_huge_pte_at()
  - Updated huge_ptep_clear_flush() to use clear_flush()
  - Track dirty bit based on returned value from get_clear_flush() in
    huge_ptep_set_access_flags()
  - Dropped Mark's reviewed-by (please re-apply if you're still happy
    with the patch)

All the dependent series ([2], [3]) for enabling contiguous hugepage
support have been merged in the previous cycle. Additionally, a patch
to clarify the semantics of huge_pte_offset() in generic code[6] is
currently in the -mm tree.

Previous postings can be found at [0], [1], [4], [5], [7].

The patches are based on v4.13-rc4. If there are no further comments
please consider merging for the next release cycle.

Thanks,
Punit

[0] https://www.spinics.net/lists/arm-kernel/msg570422.html
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/497027.html
[2] https://www.spinics.net/lists/arm-kernel/msg581657.html
[3] https://www.spinics.net/lists/arm-kernel/msg583342.html
[4] https://www.spinics.net/lists/arm-kernel/msg583367.html
[5] https://www.spinics.net/lists/arm-kernel/msg582758.html
[6] https://lkml.org/lkml/2017/7/25/536
[7] https://www.spinics.net/lists/arm-kernel/msg597777.html

Punit Agrawal (4):
  arm64: hugetlb: Handle swap entries in huge_pte_offset() for
    contiguous hugepages
  arm64: hugetlb: Override huge_pte_clear() to support contiguous
    hugepages
  arm64: hugetlb: Override set_huge_swap_pte_at() to support contiguous
    hugepages
  arm64: Re-enable support for contiguous hugepages

Steve Capper (5):
  arm64: hugetlb: set_huge_pte_at Add WARN_ON on !pte_present
  arm64: hugetlb: Introduce pte_pgprot helper
  arm64: hugetlb: Spring clean huge pte accessors
  arm64: hugetlb: Add break-before-make logic for contiguous entries
  arm64: hugetlb: Cleanup setup_hugepagesz

 arch/arm64/include/asm/hugetlb.h |   9 +-
 arch/arm64/mm/hugetlbpage.c      | 310 ++++++++++++++++++++++++++++-----------
 2 files changed, 236 insertions(+), 83 deletions(-)

-- 
2.13.2

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 1/9] arm64: hugetlb: set_huge_pte_at Add WARN_ON on !pte_present
Date: Thu, 10 Aug 2017 18:08:58 +0100
Message-Id: <20170810170906.30772-2-punit.agrawal@arm.com>
In-Reply-To: <20170810170906.30772-1-punit.agrawal@arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: will.deacon@arm.com, catalin.marinas@arm.com
Cc: Steve Capper <steve.capper@arm.com>, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, David Woods <dwoods@mellanox.com>, Punit Agrawal <punit.agrawal@arm.com>

From: Steve Capper <steve.capper@arm.com>

This patch adds a WARN_ON to set_huge_pte_at as the accessor assumes
that entries to be written down are all present. (There are separate
accessors to clear huge ptes).

We will need to handle the !pte_present case where memory offlining
is used on hugetlb pages. swap and migration entries will be supplied
to set_huge_pte_at in this case.

Cc: David Woods <dwoods@mellanox.com>
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
---
 arch/arm64/mm/hugetlbpage.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 656e0ece2289..7b61e4833432 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -67,6 +67,12 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
 	unsigned long pfn;
 	pgprot_t hugeprot;
 
+	/*
+	 * Code needs to be expanded to handle huge swap and migration
+	 * entries. Needed for HUGETLB and MEMORY_FAILURE.
+	 */
+	WARN_ON(!pte_present(pte));
+
 	if (!pte_cont(pte)) {
 		set_pte_at(mm, addr, ptep, pte);
 		return;
-- 
2.13.2

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 2/9] arm64: hugetlb: Introduce pte_pgprot helper
Date: Thu, 10 Aug 2017 18:08:59 +0100
Message-Id: <20170810170906.30772-3-punit.agrawal@arm.com>
In-Reply-To: <20170810170906.30772-1-punit.agrawal@arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: will.deacon@arm.com, catalin.marinas@arm.com
Cc: Steve Capper <steve.capper@arm.com>, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, David Woods <dwoods@mellanox.com>, Punit Agrawal <punit.agrawal@arm.com>

From: Steve Capper <steve.capper@arm.com>

Rather than xor pte bits in various places, use this helper function.

Cc: David Woods <dwoods@mellanox.com>
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
---
 arch/arm64/mm/hugetlbpage.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 7b61e4833432..cb84ca33bc6b 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -41,6 +41,16 @@ int pud_huge(pud_t pud)
 #endif
 }
 
+/*
+ * Select all bits except the pfn
+ */
+static inline pgprot_t pte_pgprot(pte_t pte)
+{
+	unsigned long pfn = pte_pfn(pte);
+
+	return __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte));
+}
+
 static int find_num_contig(struct mm_struct *mm, unsigned long addr,
 			   pte_t *ptep, size_t *pgsize)
 {
@@ -80,7 +90,7 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
 
 	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
 	pfn = pte_pfn(pte);
-	hugeprot = __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte));
+	hugeprot = pte_pgprot(pte);
 	for (i = 0; i < ncontig; i++) {
 		pr_debug("%s: set pte %p to 0x%llx\n", __func__, ptep,
 			 pte_val(pfn_pte(pfn, hugeprot)));
@@ -223,9 +233,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 		size_t pgsize = 0;
 		unsigned long pfn = pte_pfn(pte);
 		/* Select all bits except the pfn */
-		pgprot_t hugeprot =
-			__pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^
-				 pte_val(pte));
+		pgprot_t hugeprot = pte_pgprot(pte);
 
 		pfn = pte_pfn(pte);
 		ncontig = find_num_contig(vma->vm_mm, addr, ptep,
-- 
2.13.2

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 3/9] arm64: hugetlb: Spring clean huge pte accessors
Date: Thu, 10 Aug 2017 18:09:00 +0100
Message-Id: <20170810170906.30772-4-punit.agrawal@arm.com>
In-Reply-To: <20170810170906.30772-1-punit.agrawal@arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: will.deacon@arm.com, catalin.marinas@arm.com
Cc: Steve Capper <steve.capper@arm.com>, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, David Woods <dwoods@mellanox.com>, Punit Agrawal <punit.agrawal@arm.com>

From: Steve Capper <steve.capper@arm.com>

This patch aims to re-structure the huge pte accessors without affecting
their functionality. Control flow is changed to reduce indentation and
expanded use is made of post for loop variable modification.

It is then much easier to add break-before-make semantics in a subsequent
patch.

Cc: David Woods <dwoods@mellanox.com>
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
---
 arch/arm64/mm/hugetlbpage.c | 119 ++++++++++++++++++++------------------------
 1 file changed, 54 insertions(+), 65 deletions(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index cb84ca33bc6b..08deed7c71f0 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -74,7 +74,7 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
 	size_t pgsize;
 	int i;
 	int ncontig;
-	unsigned long pfn;
+	unsigned long pfn, dpfn;
 	pgprot_t hugeprot;
 
 	/*
@@ -90,14 +90,13 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
 
 	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
 	pfn = pte_pfn(pte);
+	dpfn = pgsize >> PAGE_SHIFT;
 	hugeprot = pte_pgprot(pte);
-	for (i = 0; i < ncontig; i++) {
+
+	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn) {
 		pr_debug("%s: set pte %p to 0x%llx\n", __func__, ptep,
 			 pte_val(pfn_pte(pfn, hugeprot)));
 		set_pte_at(mm, addr, ptep, pfn_pte(pfn, hugeprot));
-		ptep++;
-		pfn += pgsize >> PAGE_SHIFT;
-		addr += pgsize;
 	}
 }
 
@@ -195,91 +194,81 @@ pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
 pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 			      unsigned long addr, pte_t *ptep)
 {
-	pte_t pte;
-
-	if (pte_cont(*ptep)) {
-		int ncontig, i;
-		size_t pgsize;
-		bool is_dirty = false;
-
-		ncontig = find_num_contig(mm, addr, ptep, &pgsize);
-		/* save the 1st pte to return */
-		pte = ptep_get_and_clear(mm, addr, ptep);
-		for (i = 1, addr += pgsize; i < ncontig; ++i, addr += pgsize) {
-			/*
-			 * If HW_AFDBM is enabled, then the HW could
-			 * turn on the dirty bit for any of the page
-			 * in the set, so check them all.
-			 */
-			++ptep;
-			if (pte_dirty(ptep_get_and_clear(mm, addr, ptep)))
-				is_dirty = true;
-		}
-		if (is_dirty)
-			return pte_mkdirty(pte);
-		else
-			return pte;
-	} else {
+	int ncontig, i;
+	size_t pgsize;
+	pte_t orig_pte = huge_ptep_get(ptep);
+
+	if (!pte_cont(orig_pte))
 		return ptep_get_and_clear(mm, addr, ptep);
+
+	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
+	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) {
+		/*
+		 * If HW_AFDBM is enabled, then the HW could
+		 * turn on the dirty bit for any of the page
+		 * in the set, so check them all.
+		 */
+		if (pte_dirty(ptep_get_and_clear(mm, addr, ptep)))
+			orig_pte = pte_mkdirty(orig_pte);
 	}
+
+	return orig_pte;
 }
 
 int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 			       unsigned long addr, pte_t *ptep,
 			       pte_t pte, int dirty)
 {
-	if (pte_cont(pte)) {
-		int ncontig, i, changed = 0;
-		size_t pgsize = 0;
-		unsigned long pfn = pte_pfn(pte);
-		/* Select all bits except the pfn */
-		pgprot_t hugeprot = pte_pgprot(pte);
-
-		pfn = pte_pfn(pte);
-		ncontig = find_num_contig(vma->vm_mm, addr, ptep,
-					  &pgsize);
-		for (i = 0; i < ncontig; ++i, ++ptep, addr += pgsize) {
-			changed |= ptep_set_access_flags(vma, addr, ptep,
-							pfn_pte(pfn,
-								hugeprot),
-							dirty);
-			pfn += pgsize >> PAGE_SHIFT;
-		}
-		return changed;
-	} else {
+	int ncontig, i, changed = 0;
+	size_t pgsize = 0;
+	unsigned long pfn = pte_pfn(pte), dpfn;
+	pgprot_t hugeprot;
+
+	if (!pte_cont(pte))
 		return ptep_set_access_flags(vma, addr, ptep, pte, dirty);
+
+	ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
+	dpfn = pgsize >> PAGE_SHIFT;
+	hugeprot = pte_pgprot(pte);
+
+	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn) {
+		changed |= ptep_set_access_flags(vma, addr, ptep,
+				pfn_pte(pfn, hugeprot), dirty);
 	}
+
+	return changed;
 }
 
 void huge_ptep_set_wrprotect(struct mm_struct *mm,
 			     unsigned long addr, pte_t *ptep)
 {
-	if (pte_cont(*ptep)) {
-		int ncontig, i;
-		size_t pgsize = 0;
+	int ncontig, i;
+	size_t pgsize;
 
-		ncontig = find_num_contig(mm, addr, ptep, &pgsize);
-		for (i = 0; i < ncontig; ++i, ++ptep, addr += pgsize)
-			ptep_set_wrprotect(mm, addr, ptep);
-	} else {
+	if (!pte_cont(*ptep)) {
 		ptep_set_wrprotect(mm, addr, ptep);
+		return;
 	}
+
+	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
+	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize)
+		ptep_set_wrprotect(mm, addr, ptep);
 }
 
 void huge_ptep_clear_flush(struct vm_area_struct *vma,
 			   unsigned long addr, pte_t *ptep)
 {
-	if (pte_cont(*ptep)) {
-		int ncontig, i;
-		size_t pgsize = 0;
-
-		ncontig = find_num_contig(vma->vm_mm, addr, ptep,
-					  &pgsize);
-		for (i = 0; i < ncontig; ++i, ++ptep, addr += pgsize)
-			ptep_clear_flush(vma, addr, ptep);
-	} else {
+	int ncontig, i;
+	size_t pgsize;
+
+	if (!pte_cont(*ptep)) {
 		ptep_clear_flush(vma, addr, ptep);
+		return;
 	}
+
+	ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
+	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize)
+		ptep_clear_flush(vma, addr, ptep);
 }
 
 static __init int setup_hugepagesz(char *opt)
-- 
2.13.2

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 4/9] arm64: hugetlb: Add break-before-make logic for contiguous entries
Date: Thu, 10 Aug 2017 18:09:01 +0100
Message-Id: <20170810170906.30772-5-punit.agrawal@arm.com>
In-Reply-To: <20170810170906.30772-1-punit.agrawal@arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: will.deacon@arm.com, catalin.marinas@arm.com, mark.rutland@arm.com
Cc: Steve Capper <steve.capper@arm.com>, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, David Woods <dwoods@mellanox.com>, Punit Agrawal <punit.agrawal@arm.com>

From: Steve Capper <steve.capper@arm.com>


It has become apparent that one has to take special care when modifying
attributes of memory mappings that employ the contiguous bit.

Both the requirement and the architecturally correct "Break-Before-Make"
technique of updating contiguous entries can be found described in:
ARM DDI 0487A.k_iss10775, "Misprogramming of the Contiguous bit",
page D4-1762.

The huge pte accessors currently replace the attributes of contiguous
pte entries in place thus can, on certain platforms, lead to TLB
conflict aborts or even erroneous results returned from TLB lookups.

This patch adds two helper functions -

* get_clear_flush(.) - clears a contiguous entry and returns the head
  pte (whilst taking care to retain dirty bit information that could
  have been modified by DBM).

* clear_flush(.) that clears a contiguous entry

A tlb invalidate is performed to then ensure that there is no
possibility of multiple tlb entries being present for the same region.

Cc: David Woods <dwoods@mellanox.com>
Signed-off-by: Steve Capper <steve.capper@arm.com>
(Added helper clear_flush(), updated commit log, and comments cleanup)
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
---
Hi Mark,

I've dropped your reviewed-by tag due to the patch update. I'd
appreciate if you could take a look at the new version.

Thanks!
---
 arch/arm64/mm/hugetlbpage.c | 107 +++++++++++++++++++++++++++++++++++---------
 1 file changed, 86 insertions(+), 21 deletions(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 08deed7c71f0..d3a6713048a2 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -68,6 +68,62 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
 	return CONT_PTES;
 }
 
+/*
+ * Changing some bits of contiguous entries requires us to follow a
+ * Break-Before-Make approach, breaking the whole contiguous set
+ * before we can change any entries. See ARM DDI 0487A.k_iss10775,
+ * "Misprogramming of the Contiguous bit", page D4-1762.
+ *
+ * This helper performs the break step.
+ */
+static pte_t get_clear_flush(struct mm_struct *mm,
+			     unsigned long addr,
+			     pte_t *ptep,
+			     unsigned long pgsize,
+			     unsigned long ncontig)
+{
+	unsigned long i, saddr = addr;
+	struct vm_area_struct vma = { .vm_mm = mm };
+	pte_t orig_pte = huge_ptep_get(ptep);
+
+	/*
+	 * If we already have a faulting entry then we don't need
+	 * to break before make (there won't be a tlb entry cached).
+	 */
+	if (!pte_present(orig_pte))
+		return orig_pte;
+
+	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) {
+		pte_t pte = ptep_get_and_clear(mm, addr, ptep);
+
+		/*
+		 * If HW_AFDBM is enabled, then the HW could turn on
+		 * the dirty bit for any page in the set, so check
+		 * them all.  All hugetlb entries are already young.
+		 */
+		if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM) && pte_dirty(pte))
+			orig_pte = pte_mkdirty(orig_pte);
+	}
+
+	flush_tlb_range(&vma, saddr, addr);
+	return orig_pte;
+}
+
+static void clear_flush(struct mm_struct *mm,
+			     unsigned long addr,
+			     pte_t *ptep,
+			     unsigned long pgsize,
+			     unsigned long ncontig)
+{
+	unsigned long i, saddr = addr;
+	struct vm_area_struct vma = { .vm_mm = mm };
+
+	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++)
+		pte_clear(mm, addr, ptep);
+
+	flush_tlb_range(&vma, saddr, addr);
+}
+
 void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
 			    pte_t *ptep, pte_t pte)
 {
@@ -93,6 +149,8 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
 	dpfn = pgsize >> PAGE_SHIFT;
 	hugeprot = pte_pgprot(pte);
 
+	clear_flush(mm, addr, ptep, pgsize, ncontig);
+
 	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn) {
 		pr_debug("%s: set pte %p to 0x%llx\n", __func__, ptep,
 			 pte_val(pfn_pte(pfn, hugeprot)));
@@ -194,7 +252,7 @@ pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
 pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 			      unsigned long addr, pte_t *ptep)
 {
-	int ncontig, i;
+	int ncontig;
 	size_t pgsize;
 	pte_t orig_pte = huge_ptep_get(ptep);
 
@@ -202,17 +260,8 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 		return ptep_get_and_clear(mm, addr, ptep);
 
 	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
-	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) {
-		/*
-		 * If HW_AFDBM is enabled, then the HW could
-		 * turn on the dirty bit for any of the page
-		 * in the set, so check them all.
-		 */
-		if (pte_dirty(ptep_get_and_clear(mm, addr, ptep)))
-			orig_pte = pte_mkdirty(orig_pte);
-	}
 
-	return orig_pte;
+	return get_clear_flush(mm, addr, ptep, pgsize, ncontig);
 }
 
 int huge_ptep_set_access_flags(struct vm_area_struct *vma,
@@ -222,6 +271,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 	int ncontig, i, changed = 0;
 	size_t pgsize = 0;
 	unsigned long pfn = pte_pfn(pte), dpfn;
+	pte_t orig_pte;
 	pgprot_t hugeprot;
 
 	if (!pte_cont(pte))
@@ -229,12 +279,18 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 
 	ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
 	dpfn = pgsize >> PAGE_SHIFT;
-	hugeprot = pte_pgprot(pte);
 
-	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn) {
-		changed |= ptep_set_access_flags(vma, addr, ptep,
-				pfn_pte(pfn, hugeprot), dirty);
-	}
+	orig_pte = get_clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig);
+	if (!pte_same(orig_pte, pte))
+		changed = 1;
+
+	/* Make sure we don't lose the dirty state */
+	if (pte_dirty(orig_pte))
+		pte = pte_mkdirty(pte);
+
+	hugeprot = pte_pgprot(pte);
+	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
+		set_pte_at(vma->vm_mm, addr, ptep, pfn_pte(pfn, hugeprot));
 
 	return changed;
 }
@@ -244,6 +300,9 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm,
 {
 	int ncontig, i;
 	size_t pgsize;
+	pte_t pte = pte_wrprotect(huge_ptep_get(ptep)), orig_pte;
+	unsigned long pfn = pte_pfn(pte), dpfn;
+	pgprot_t hugeprot;
 
 	if (!pte_cont(*ptep)) {
 		ptep_set_wrprotect(mm, addr, ptep);
@@ -251,14 +310,21 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm,
 	}
 
 	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
-	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize)
-		ptep_set_wrprotect(mm, addr, ptep);
+	dpfn = pgsize >> PAGE_SHIFT;
+
+	orig_pte = get_clear_flush(mm, addr, ptep, pgsize, ncontig);
+	if (pte_dirty(orig_pte))
+		pte = pte_mkdirty(pte);
+
+	hugeprot = pte_pgprot(pte);
+	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
+		set_pte_at(mm, addr, ptep, pfn_pte(pfn, hugeprot));
 }
 
 void huge_ptep_clear_flush(struct vm_area_struct *vma,
 			   unsigned long addr, pte_t *ptep)
 {
-	int ncontig, i;
+	int ncontig;
 	size_t pgsize;
 
 	if (!pte_cont(*ptep)) {
@@ -267,8 +333,7 @@ void huge_ptep_clear_flush(struct vm_area_struct *vma,
 	}
 
 	ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
-	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize)
-		ptep_clear_flush(vma, addr, ptep);
+	clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig);
 }
 
 static __init int setup_hugepagesz(char *opt)
-- 
2.13.2

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 5/9] arm64: hugetlb: Handle swap entries in huge_pte_offset() for contiguous hugepages
Date: Thu, 10 Aug 2017 18:09:02 +0100
Message-Id: <20170810170906.30772-6-punit.agrawal@arm.com>
In-Reply-To: <20170810170906.30772-1-punit.agrawal@arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: will.deacon@arm.com, catalin.marinas@arm.com
Cc: Punit Agrawal <punit.agrawal@arm.com>, linux-mm@kvack.org, steve.capper@arm.com, linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, David Woods <dwoods@mellanox.com>

huge_pte_offset() was updated to correctly handle swap entries for
hugepages. With the addition of the size parameter, it is now possible
to disambiguate whether the request is for a regular hugepage or a
contiguous hugepage.

Fix huge_pte_offset() for contiguous hugepages by using the size to find
the correct page table entry.

Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Cc: David Woods <dwoods@mellanox.com>
---
 arch/arm64/mm/hugetlbpage.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index d3a6713048a2..09e79785c019 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -210,6 +210,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
+	pte_t *pte;
 
 	pgd = pgd_offset(mm, addr);
 	pr_debug("%s: addr:0x%lx pgd:%p\n", __func__, addr, pgd);
@@ -217,19 +218,29 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
 		return NULL;
 
 	pud = pud_offset(pgd, addr);
-	if (pud_none(*pud))
+	if (pud_none(*pud) && sz != PUD_SIZE)
 		return NULL;
 	/* swap or huge page */
 	if (!pud_present(*pud) || pud_huge(*pud))
 		return (pte_t *)pud;
 	/* table; check the next level */
 
+	if (sz == CONT_PMD_SIZE)
+		addr &= CONT_PMD_MASK;
+
 	pmd = pmd_offset(pud, addr);
-	if (pmd_none(*pmd))
+	if (pmd_none(*pmd) &&
+	    !(sz == PMD_SIZE || sz == CONT_PMD_SIZE))
 		return NULL;
 	if (!pmd_present(*pmd) || pmd_huge(*pmd))
 		return (pte_t *)pmd;
 
+	if (sz == CONT_PTE_SIZE) {
+		pte = pte_offset_kernel(
+			pmd, (addr & CONT_PTE_MASK));
+		return pte;
+	}
+
 	return NULL;
 }
 
-- 
2.13.2

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 6/9] arm64: hugetlb: Override huge_pte_clear() to support contiguous hugepages
Date: Thu, 10 Aug 2017 18:09:03 +0100
Message-Id: <20170810170906.30772-7-punit.agrawal@arm.com>
In-Reply-To: <20170810170906.30772-1-punit.agrawal@arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: will.deacon@arm.com, catalin.marinas@arm.com
Cc: Punit Agrawal <punit.agrawal@arm.com>, linux-mm@kvack.org, steve.capper@arm.com, linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, David Woods <dwoods@mellanox.com>

The default huge_pte_clear() implementation does not clear contiguous
page table entries when it encounters contiguous hugepages that are
supported on arm64.

Fix this by overriding the default implementation to clear all the
entries associated with contiguous hugepages.

Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Cc: David Woods <dwoods@mellanox.com>
---
 arch/arm64/include/asm/hugetlb.h |  6 +++++-
 arch/arm64/mm/hugetlbpage.c      | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
index 793bd73b0d07..df8c0aea0917 100644
--- a/arch/arm64/include/asm/hugetlb.h
+++ b/arch/arm64/include/asm/hugetlb.h
@@ -18,7 +18,6 @@
 #ifndef __ASM_HUGETLB_H
 #define __ASM_HUGETLB_H
 
-#include <asm-generic/hugetlb.h>
 #include <asm/page.h>
 
 static inline pte_t huge_ptep_get(pte_t *ptep)
@@ -82,6 +81,11 @@ extern void huge_ptep_set_wrprotect(struct mm_struct *mm,
 				    unsigned long addr, pte_t *ptep);
 extern void huge_ptep_clear_flush(struct vm_area_struct *vma,
 				  unsigned long addr, pte_t *ptep);
+extern void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
+			   pte_t *ptep, unsigned long sz);
+#define huge_pte_clear huge_pte_clear
+
+#include <asm-generic/hugetlb.h>
 
 #ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
 static inline bool gigantic_page_supported(void) { return true; }
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 09e79785c019..b69430a04e87 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -68,6 +68,30 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
 	return CONT_PTES;
 }
 
+static inline int num_contig_ptes(unsigned long size, size_t *pgsize)
+{
+	int contig_ptes = 0;
+
+	*pgsize = size;
+
+	switch (size) {
+	case PUD_SIZE:
+	case PMD_SIZE:
+		contig_ptes = 1;
+		break;
+	case CONT_PMD_SIZE:
+		*pgsize = PMD_SIZE;
+		contig_ptes = CONT_PMDS;
+		break;
+	case CONT_PTE_SIZE:
+		*pgsize = PAGE_SIZE;
+		contig_ptes = CONT_PTES;
+		break;
+	}
+
+	return contig_ptes;
+}
+
 /*
  * Changing some bits of contiguous entries requires us to follow a
  * Break-Before-Make approach, breaking the whole contiguous set
@@ -260,6 +284,18 @@ pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
 	return entry;
 }
 
+void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
+		    pte_t *ptep, unsigned long sz)
+{
+	int i, ncontig;
+	size_t pgsize;
+
+	ncontig = num_contig_ptes(sz, &pgsize);
+
+	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++)
+		pte_clear(mm, addr, ptep);
+}
+
 pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 			      unsigned long addr, pte_t *ptep)
 {
-- 
2.13.2

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 7/9] arm64: hugetlb: Override set_huge_swap_pte_at() to support contiguous hugepages
Date: Thu, 10 Aug 2017 18:09:04 +0100
Message-Id: <20170810170906.30772-8-punit.agrawal@arm.com>
In-Reply-To: <20170810170906.30772-1-punit.agrawal@arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: will.deacon@arm.com, catalin.marinas@arm.com
Cc: Punit Agrawal <punit.agrawal@arm.com>, linux-mm@kvack.org, steve.capper@arm.com, linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, David Woods <dwoods@mellanox.com>

The default implementation of set_huge_swap_pte_at() does not support
hugepages consisting of contiguous ptes. Override it to add support for
contiguous hugepages.

Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Cc: David Woods <dwoods@mellanox.com>
---
 arch/arm64/include/asm/hugetlb.h |  3 +++
 arch/arm64/mm/hugetlbpage.c      | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
index df8c0aea0917..1dca41bea16a 100644
--- a/arch/arm64/include/asm/hugetlb.h
+++ b/arch/arm64/include/asm/hugetlb.h
@@ -84,6 +84,9 @@ extern void huge_ptep_clear_flush(struct vm_area_struct *vma,
 extern void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
 			   pte_t *ptep, unsigned long sz);
 #define huge_pte_clear huge_pte_clear
+extern void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr,
+				 pte_t *ptep, pte_t pte, unsigned long sz);
+#define set_huge_swap_pte_at set_huge_swap_pte_at
 
 #include <asm-generic/hugetlb.h>
 
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index b69430a04e87..f6b2ef23285d 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -182,6 +182,18 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
 	}
 }
 
+void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr,
+			  pte_t *ptep, pte_t pte, unsigned long sz)
+{
+	int i, ncontig;
+	size_t pgsize;
+
+	ncontig = num_contig_ptes(sz, &pgsize);
+
+	for (i = 0; i < ncontig; i++, ptep++)
+		set_pte(ptep, pte);
+}
+
 pte_t *huge_pte_alloc(struct mm_struct *mm,
 		      unsigned long addr, unsigned long sz)
 {
-- 
2.13.2

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 8/9] arm64: Re-enable support for contiguous hugepages
Date: Thu, 10 Aug 2017 18:09:05 +0100
Message-Id: <20170810170906.30772-9-punit.agrawal@arm.com>
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Cc: Punit Agrawal <punit.agrawal@arm.com>, linux-mm@kvack.org, steve.capper@arm.com, linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com

also known as -

Revert "Revert "Revert "arm64: hugetlb: partial revert of 66b3923a1a0f"""

Now that our hugetlb implementation is compliant with the
break-before-make requirements of the architecture and we have addressed
some of the issues in core code required for properly dealing with
hardware poisoning of contiguous hugepages let's re-enable support for
contiguous hugepages.

This reverts commit 6ae979ab39a368c18ceb0424bf824d172d6ab56f.

Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
---
 arch/arm64/mm/hugetlbpage.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index f6b2ef23285d..273f126072e4 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -403,6 +403,10 @@ static __init int setup_hugepagesz(char *opt)
 		hugetlb_add_hstate(PMD_SHIFT - PAGE_SHIFT);
 	} else if (ps == PUD_SIZE) {
 		hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
+	} else if (ps == (PAGE_SIZE * CONT_PTES)) {
+		hugetlb_add_hstate(CONT_PTE_SHIFT);
+	} else if (ps == (PMD_SIZE * CONT_PMDS)) {
+		hugetlb_add_hstate((PMD_SHIFT + CONT_PMD_SHIFT) - PAGE_SHIFT);
 	} else {
 		hugetlb_bad_size();
 		pr_err("hugepagesz: Unsupported page size %lu K\n", ps >> 10);
@@ -411,3 +415,13 @@ static __init int setup_hugepagesz(char *opt)
 	return 1;
 }
 __setup("hugepagesz=", setup_hugepagesz);
+
+#ifdef CONFIG_ARM64_64K_PAGES
+static __init int add_default_hugepagesz(void)
+{
+	if (size_to_hstate(CONT_PTES * PAGE_SIZE) == NULL)
+		hugetlb_add_hstate(CONT_PTE_SHIFT);
+	return 0;
+}
+arch_initcall(add_default_hugepagesz);
+#endif
-- 
2.13.2

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: [PATCH v6 9/9] arm64: hugetlb: Cleanup setup_hugepagesz
Date: Thu, 10 Aug 2017 18:09:06 +0100
Message-Id: <20170810170906.30772-10-punit.agrawal@arm.com>
In-Reply-To: <20170810170906.30772-1-punit.agrawal@arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: will.deacon@arm.com, catalin.marinas@arm.com
Cc: Steve Capper <steve.capper@arm.com>, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, David Woods <dwoods@mellanox.com>, stable@vger.kernel.org, Punit Agrawal <punit.agrawal@arm.com>

From: Steve Capper <steve.capper@arm.com>

Replace a lot of if statements with switch and case labels to make it
much clearer which huge page sizes are supported.

Also, we prevent PUD_SIZE from being used on systems not running with
4KB PAGE_SIZE. Before if one supplied PUD_SIZE in these circumstances,
then unusuable huge page sizes would be in use.

Fixes: 084bd29810a5 ("ARM64: mm: HugeTLB support.")
Cc: David Woods <dwoods@mellanox.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
---
 arch/arm64/mm/hugetlbpage.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 273f126072e4..2c9913121bfd 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -399,20 +399,20 @@ static __init int setup_hugepagesz(char *opt)
 {
 	unsigned long ps = memparse(opt, &opt);
 
-	if (ps == PMD_SIZE) {
-		hugetlb_add_hstate(PMD_SHIFT - PAGE_SHIFT);
-	} else if (ps == PUD_SIZE) {
-		hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
-	} else if (ps == (PAGE_SIZE * CONT_PTES)) {
-		hugetlb_add_hstate(CONT_PTE_SHIFT);
-	} else if (ps == (PMD_SIZE * CONT_PMDS)) {
-		hugetlb_add_hstate((PMD_SHIFT + CONT_PMD_SHIFT) - PAGE_SHIFT);
-	} else {
-		hugetlb_bad_size();
-		pr_err("hugepagesz: Unsupported page size %lu K\n", ps >> 10);
-		return 0;
+	switch (ps) {
+#ifdef CONFIG_ARM64_4K_PAGES
+	case PUD_SIZE:
+#endif
+	case PMD_SIZE * CONT_PMDS:
+	case PMD_SIZE:
+	case PAGE_SIZE * CONT_PTES:
+		hugetlb_add_hstate(ilog2(ps) - PAGE_SHIFT);
+		return 1;
 	}
-	return 1;
+
+	hugetlb_bad_size();
+	pr_err("hugepagesz: Unsupported page size %lu K\n", ps >> 10);
+	return 0;
 }
 __setup("hugepagesz=", setup_hugepagesz);
 
-- 
2.13.2

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Date: Thu, 17 Aug 2017 19:03:11 +0100
From: Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH v6 4/9] arm64: hugetlb: Add break-before-make logic for
 contiguous entries
Message-ID: <20170817180311.uwrz64g3bkwfdkrn@armageddon.cambridge.arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
 <20170810170906.30772-5-punit.agrawal@arm.com>
MIME-Version: 1.0
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To: Punit Agrawal <punit.agrawal@arm.com>
Cc: will.deacon@arm.com, mark.rutland@arm.com, linux-mm@kvack.org, David Woods <dwoods@mellanox.com>, linux-arm-kernel@lists.infradead.org, Steve Capper <steve.capper@arm.com>

On Thu, Aug 10, 2017 at 06:09:01PM +0100, Punit Agrawal wrote:
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -68,6 +68,62 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
>  	return CONT_PTES;
>  }
>  
> +/*
> + * Changing some bits of contiguous entries requires us to follow a
> + * Break-Before-Make approach, breaking the whole contiguous set
> + * before we can change any entries. See ARM DDI 0487A.k_iss10775,
> + * "Misprogramming of the Contiguous bit", page D4-1762.
> + *
> + * This helper performs the break step.
> + */
> +static pte_t get_clear_flush(struct mm_struct *mm,
> +			     unsigned long addr,
> +			     pte_t *ptep,
> +			     unsigned long pgsize,
> +			     unsigned long ncontig)
> +{
> +	unsigned long i, saddr = addr;
> +	struct vm_area_struct vma = { .vm_mm = mm };
> +	pte_t orig_pte = huge_ptep_get(ptep);
> +
> +	/*
> +	 * If we already have a faulting entry then we don't need
> +	 * to break before make (there won't be a tlb entry cached).
> +	 */
> +	if (!pte_present(orig_pte))
> +		return orig_pte;

I first thought we could relax this check to pte_valid() as we don't
care about the PROT_NONE case for hardware page table updates. However,
I realised that we call this where we expect the pte to be entirely
cleared but we simply skip it if !present (e.g. swap entry). Is this
correct?

> +
> +	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) {
> +		pte_t pte = ptep_get_and_clear(mm, addr, ptep);
> +
> +		/*
> +		 * If HW_AFDBM is enabled, then the HW could turn on
> +		 * the dirty bit for any page in the set, so check
> +		 * them all.  All hugetlb entries are already young.
> +		 */
> +		if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM) && pte_dirty(pte))
> +			orig_pte = pte_mkdirty(orig_pte);
> +	}
> +
> +	flush_tlb_range(&vma, saddr, addr);
> +	return orig_pte;
> +}

It would be better if you do something like

	bool valid = pte_valid(org_pte);
	...
	if (valid)
		flush_tlb_range(...);

> +
> +static void clear_flush(struct mm_struct *mm,
> +			     unsigned long addr,
> +			     pte_t *ptep,
> +			     unsigned long pgsize,
> +			     unsigned long ncontig)
> +{
> +	unsigned long i, saddr = addr;
> +	struct vm_area_struct vma = { .vm_mm = mm };
> +
> +	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++)
> +		pte_clear(mm, addr, ptep);
> +
> +	flush_tlb_range(&vma, saddr, addr);
> +}
> +
>  void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
>  			    pte_t *ptep, pte_t pte)
>  {
> @@ -93,6 +149,8 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
>  	dpfn = pgsize >> PAGE_SHIFT;
>  	hugeprot = pte_pgprot(pte);
>  
> +	clear_flush(mm, addr, ptep, pgsize, ncontig);
> +
>  	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn) {
>  		pr_debug("%s: set pte %p to 0x%llx\n", __func__, ptep,
>  			 pte_val(pfn_pte(pfn, hugeprot)));
> @@ -194,7 +252,7 @@ pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
>  pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
>  			      unsigned long addr, pte_t *ptep)
>  {
> -	int ncontig, i;
> +	int ncontig;
>  	size_t pgsize;
>  	pte_t orig_pte = huge_ptep_get(ptep);
>  
> @@ -202,17 +260,8 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
>  		return ptep_get_and_clear(mm, addr, ptep);
>  
>  	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
> -	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) {
> -		/*
> -		 * If HW_AFDBM is enabled, then the HW could
> -		 * turn on the dirty bit for any of the page
> -		 * in the set, so check them all.
> -		 */
> -		if (pte_dirty(ptep_get_and_clear(mm, addr, ptep)))
> -			orig_pte = pte_mkdirty(orig_pte);
> -	}
>  
> -	return orig_pte;
> +	return get_clear_flush(mm, addr, ptep, pgsize, ncontig);
>  }

E.g. here you don't always clear the pte if a swap entry.

>  
>  int huge_ptep_set_access_flags(struct vm_area_struct *vma,
> @@ -222,6 +271,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
>  	int ncontig, i, changed = 0;
>  	size_t pgsize = 0;
>  	unsigned long pfn = pte_pfn(pte), dpfn;
> +	pte_t orig_pte;
>  	pgprot_t hugeprot;
>  
>  	if (!pte_cont(pte))
> @@ -229,12 +279,18 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
>  
>  	ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
>  	dpfn = pgsize >> PAGE_SHIFT;
> -	hugeprot = pte_pgprot(pte);
>  
> -	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn) {
> -		changed |= ptep_set_access_flags(vma, addr, ptep,
> -				pfn_pte(pfn, hugeprot), dirty);
> -	}
> +	orig_pte = get_clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig);
> +	if (!pte_same(orig_pte, pte))
> +		changed = 1;
> +
> +	/* Make sure we don't lose the dirty state */
> +	if (pte_dirty(orig_pte))
> +		pte = pte_mkdirty(pte);
> +
> +	hugeprot = pte_pgprot(pte);
> +	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
> +		set_pte_at(vma->vm_mm, addr, ptep, pfn_pte(pfn, hugeprot));
>  
>  	return changed;
>  }
> @@ -244,6 +300,9 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm,
>  {
>  	int ncontig, i;
>  	size_t pgsize;
> +	pte_t pte = pte_wrprotect(huge_ptep_get(ptep)), orig_pte;

I'm not particularly fond of too many function calls in the variable
initialisation part. I would rather keep pte_wrprotect further down
where you also make it "dirty".

> +	unsigned long pfn = pte_pfn(pte), dpfn;
> +	pgprot_t hugeprot;
>  
>  	if (!pte_cont(*ptep)) {
>  		ptep_set_wrprotect(mm, addr, ptep);
> @@ -251,14 +310,21 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm,
>  	}
>  
>  	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
> -	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize)
> -		ptep_set_wrprotect(mm, addr, ptep);
> +	dpfn = pgsize >> PAGE_SHIFT;
> +
> +	orig_pte = get_clear_flush(mm, addr, ptep, pgsize, ncontig);

Can you not use just set pte here instead of deriving it from *ptep
early on?

	pte = get_clear_flush(mm, addr, ptep, pgsize, ncontig);
	pte = pte_wrprotect(pte);

> +	if (pte_dirty(orig_pte))
> +		pte = pte_mkdirty(pte);
> +
> +	hugeprot = pte_pgprot(pte);
> +	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
> +		set_pte_at(mm, addr, ptep, pfn_pte(pfn, hugeprot));
>  }

-- 
Catalin

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: Re: [PATCH v6 4/9] arm64: hugetlb: Add break-before-make logic for contiguous entries
References: <20170810170906.30772-1-punit.agrawal@arm.com>
	<20170810170906.30772-5-punit.agrawal@arm.com>
	<20170817180311.uwrz64g3bkwfdkrn@armageddon.cambridge.arm.com>
Date: Fri, 18 Aug 2017 11:30:22 +0100
In-Reply-To: <20170817180311.uwrz64g3bkwfdkrn@armageddon.cambridge.arm.com>
	(Catalin Marinas's message of "Thu, 17 Aug 2017 19:03:11 +0100")
Message-ID: <87shgpnp6p.fsf@e105922-lin.cambridge.arm.com>
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To: Catalin Marinas <catalin.marinas@arm.com>
Cc: will.deacon@arm.com, mark.rutland@arm.com, linux-mm@kvack.org, David Woods <dwoods@mellanox.com>, linux-arm-kernel@lists.infradead.org, Steve Capper <steve.capper@arm.com>

Catalin Marinas <catalin.marinas@arm.com> writes:

> On Thu, Aug 10, 2017 at 06:09:01PM +0100, Punit Agrawal wrote:
>> --- a/arch/arm64/mm/hugetlbpage.c
>> +++ b/arch/arm64/mm/hugetlbpage.c
>> @@ -68,6 +68,62 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
>>  	return CONT_PTES;
>>  }
>>  
>> +/*
>> + * Changing some bits of contiguous entries requires us to follow a
>> + * Break-Before-Make approach, breaking the whole contiguous set
>> + * before we can change any entries. See ARM DDI 0487A.k_iss10775,
>> + * "Misprogramming of the Contiguous bit", page D4-1762.
>> + *
>> + * This helper performs the break step.
>> + */
>> +static pte_t get_clear_flush(struct mm_struct *mm,
>> +			     unsigned long addr,
>> +			     pte_t *ptep,
>> +			     unsigned long pgsize,
>> +			     unsigned long ncontig)
>> +{
>> +	unsigned long i, saddr = addr;
>> +	struct vm_area_struct vma = { .vm_mm = mm };
>> +	pte_t orig_pte = huge_ptep_get(ptep);
>> +
>> +	/*
>> +	 * If we already have a faulting entry then we don't need
>> +	 * to break before make (there won't be a tlb entry cached).
>> +	 */
>> +	if (!pte_present(orig_pte))
>> +		return orig_pte;
>
> I first thought we could relax this check to pte_valid() as we don't
> care about the PROT_NONE case for hardware page table updates. However,
> I realised that we call this where we expect the pte to be entirely
> cleared but we simply skip it if !present (e.g. swap entry). Is this
> correct?

I've checked back and come to the conclusion that get_clear_flush() will
not get called with swap entries.

In the case of huge_ptep_get_and_clear() below, the callers
(__unmap_hugepage_range() and hugetlb_change_protection()) check for
swap entries before calling. Similarly 

I'll relax the check to pte_valid().

>
>> +
>> +	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) {
>> +		pte_t pte = ptep_get_and_clear(mm, addr, ptep);
>> +
>> +		/*
>> +		 * If HW_AFDBM is enabled, then the HW could turn on
>> +		 * the dirty bit for any page in the set, so check
>> +		 * them all.  All hugetlb entries are already young.
>> +		 */
>> +		if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM) && pte_dirty(pte))
>> +			orig_pte = pte_mkdirty(orig_pte);
>> +	}
>> +
>> +	flush_tlb_range(&vma, saddr, addr);
>> +	return orig_pte;
>> +}
>
> It would be better if you do something like
>
> 	bool valid = pte_valid(org_pte);
> 	...
> 	if (valid)
> 		flush_tlb_range(...);

With the above change of pte_present() to pte_valid() this isn't needed
anymore.

>
>> +
>> +static void clear_flush(struct mm_struct *mm,
>> +			     unsigned long addr,
>> +			     pte_t *ptep,
>> +			     unsigned long pgsize,
>> +			     unsigned long ncontig)
>> +{
>> +	unsigned long i, saddr = addr;
>> +	struct vm_area_struct vma = { .vm_mm = mm };
>> +
>> +	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++)
>> +		pte_clear(mm, addr, ptep);
>> +
>> +	flush_tlb_range(&vma, saddr, addr);
>> +}
>> +
>>  void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
>>  			    pte_t *ptep, pte_t pte)
>>  {
>> @@ -93,6 +149,8 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
>>  	dpfn = pgsize >> PAGE_SHIFT;
>>  	hugeprot = pte_pgprot(pte);
>>  
>> +	clear_flush(mm, addr, ptep, pgsize, ncontig);
>> +
>>  	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn) {
>>  		pr_debug("%s: set pte %p to 0x%llx\n", __func__, ptep,
>>  			 pte_val(pfn_pte(pfn, hugeprot)));
>> @@ -194,7 +252,7 @@ pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
>>  pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
>>  			      unsigned long addr, pte_t *ptep)
>>  {
>> -	int ncontig, i;
>> +	int ncontig;
>>  	size_t pgsize;
>>  	pte_t orig_pte = huge_ptep_get(ptep);
>>  
>> @@ -202,17 +260,8 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
>>  		return ptep_get_and_clear(mm, addr, ptep);
>>  
>>  	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
>> -	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) {
>> -		/*
>> -		 * If HW_AFDBM is enabled, then the HW could
>> -		 * turn on the dirty bit for any of the page
>> -		 * in the set, so check them all.
>> -		 */
>> -		if (pte_dirty(ptep_get_and_clear(mm, addr, ptep)))
>> -			orig_pte = pte_mkdirty(orig_pte);
>> -	}
>>  
>> -	return orig_pte;
>> +	return get_clear_flush(mm, addr, ptep, pgsize, ncontig);
>>  }
>
> E.g. here you don't always clear the pte if a swap entry.
>
>>  
>>  int huge_ptep_set_access_flags(struct vm_area_struct *vma,
>> @@ -222,6 +271,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
>>  	int ncontig, i, changed = 0;
>>  	size_t pgsize = 0;
>>  	unsigned long pfn = pte_pfn(pte), dpfn;
>> +	pte_t orig_pte;
>>  	pgprot_t hugeprot;
>>  
>>  	if (!pte_cont(pte))
>> @@ -229,12 +279,18 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
>>  
>>  	ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
>>  	dpfn = pgsize >> PAGE_SHIFT;
>> -	hugeprot = pte_pgprot(pte);
>>  
>> -	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn) {
>> -		changed |= ptep_set_access_flags(vma, addr, ptep,
>> -				pfn_pte(pfn, hugeprot), dirty);
>> -	}
>> +	orig_pte = get_clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig);
>> +	if (!pte_same(orig_pte, pte))
>> +		changed = 1;
>> +
>> +	/* Make sure we don't lose the dirty state */
>> +	if (pte_dirty(orig_pte))
>> +		pte = pte_mkdirty(pte);
>> +
>> +	hugeprot = pte_pgprot(pte);
>> +	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
>> +		set_pte_at(vma->vm_mm, addr, ptep, pfn_pte(pfn, hugeprot));
>>  
>>  	return changed;
>>  }
>> @@ -244,6 +300,9 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm,
>>  {
>>  	int ncontig, i;
>>  	size_t pgsize;
>> +	pte_t pte = pte_wrprotect(huge_ptep_get(ptep)), orig_pte;
>
> I'm not particularly fond of too many function calls in the variable
> initialisation part. I would rather keep pte_wrprotect further down
> where you also make it "dirty".
>
>> +	unsigned long pfn = pte_pfn(pte), dpfn;
>> +	pgprot_t hugeprot;
>>  
>>  	if (!pte_cont(*ptep)) {
>>  		ptep_set_wrprotect(mm, addr, ptep);
>> @@ -251,14 +310,21 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm,
>>  	}
>>  
>>  	ncontig = find_num_contig(mm, addr, ptep, &pgsize);
>> -	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize)
>> -		ptep_set_wrprotect(mm, addr, ptep);
>> +	dpfn = pgsize >> PAGE_SHIFT;
>> +
>> +	orig_pte = get_clear_flush(mm, addr, ptep, pgsize, ncontig);
>
> Can you not use just set pte here instead of deriving it from *ptep
> early on?
>
> 	pte = get_clear_flush(mm, addr, ptep, pgsize, ncontig);
> 	pte = pte_wrprotect(pte);
>

I've simplified this locally now.

I'll run through a few tests and post a new version.

Thanks for review.
Punit

>> +	if (pte_dirty(orig_pte))
>> +		pte = pte_mkdirty(pte);
>> +
>> +	hugeprot = pte_pgprot(pte);
>> +	for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
>> +		set_pte_at(mm, addr, ptep, pfn_pte(pfn, hugeprot));
>>  }

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Date: Fri, 18 Aug 2017 11:43:28 +0100
From: Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH v6 4/9] arm64: hugetlb: Add break-before-make logic for
 contiguous entries
Message-ID: <20170818104327.a5yep2p3ntjbffug@armageddon.cambridge.arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
 <20170810170906.30772-5-punit.agrawal@arm.com>
 <20170817180311.uwrz64g3bkwfdkrn@armageddon.cambridge.arm.com>
 <87shgpnp6p.fsf@e105922-lin.cambridge.arm.com>
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To: Punit Agrawal <punit.agrawal@arm.com>
Cc: mark.rutland@arm.com, David Woods <dwoods@mellanox.com>, Steve Capper <steve.capper@arm.com>, will.deacon@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org

On Fri, Aug 18, 2017 at 11:30:22AM +0100, Punit Agrawal wrote:
> Catalin Marinas <catalin.marinas@arm.com> writes:
> 
> > On Thu, Aug 10, 2017 at 06:09:01PM +0100, Punit Agrawal wrote:
> >> --- a/arch/arm64/mm/hugetlbpage.c
> >> +++ b/arch/arm64/mm/hugetlbpage.c
> >> @@ -68,6 +68,62 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
> >>  	return CONT_PTES;
> >>  }
> >>  
> >> +/*
> >> + * Changing some bits of contiguous entries requires us to follow a
> >> + * Break-Before-Make approach, breaking the whole contiguous set
> >> + * before we can change any entries. See ARM DDI 0487A.k_iss10775,
> >> + * "Misprogramming of the Contiguous bit", page D4-1762.
> >> + *
> >> + * This helper performs the break step.
> >> + */
> >> +static pte_t get_clear_flush(struct mm_struct *mm,
> >> +			     unsigned long addr,
> >> +			     pte_t *ptep,
> >> +			     unsigned long pgsize,
> >> +			     unsigned long ncontig)
> >> +{
> >> +	unsigned long i, saddr = addr;
> >> +	struct vm_area_struct vma = { .vm_mm = mm };
> >> +	pte_t orig_pte = huge_ptep_get(ptep);
> >> +
> >> +	/*
> >> +	 * If we already have a faulting entry then we don't need
> >> +	 * to break before make (there won't be a tlb entry cached).
> >> +	 */
> >> +	if (!pte_present(orig_pte))
> >> +		return orig_pte;
> >
> > I first thought we could relax this check to pte_valid() as we don't
> > care about the PROT_NONE case for hardware page table updates. However,
> > I realised that we call this where we expect the pte to be entirely
> > cleared but we simply skip it if !present (e.g. swap entry). Is this
> > correct?
> 
> I've checked back and come to the conclusion that get_clear_flush() will
> not get called with swap entries.
> 
> In the case of huge_ptep_get_and_clear() below, the callers
> (__unmap_hugepage_range() and hugetlb_change_protection()) check for
> swap entries before calling. Similarly 
> 
> I'll relax the check to pte_valid().

Thanks for checking but I would still keep the semantics of the generic
huge_ptep_get_and_clear() where the entry is always zeroed. It shouldn't
have any performance impact since this function won't be called for swap
entries, but just in case anyone changes the core code later on.

-- 
Catalin

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Date: Fri, 18 Aug 2017 12:20:16 +0100
From: Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH v6 5/9] arm64: hugetlb: Handle swap entries in
 huge_pte_offset() for contiguous hugepages
Message-ID: <20170818112015.2cvkb7y3gkozz5ip@armageddon.cambridge.arm.com>
References: <20170810170906.30772-1-punit.agrawal@arm.com>
 <20170810170906.30772-6-punit.agrawal@arm.com>
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List-ID: <linux-mm.kvack.org>
To: Punit Agrawal <punit.agrawal@arm.com>
Cc: will.deacon@arm.com, mark.rutland@arm.com, David Woods <dwoods@mellanox.com>, steve.capper@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org

On Thu, Aug 10, 2017 at 06:09:02PM +0100, Punit Agrawal wrote:
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index d3a6713048a2..09e79785c019 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -210,6 +210,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
>  	pgd_t *pgd;
>  	pud_t *pud;
>  	pmd_t *pmd;
> +	pte_t *pte;
>  
>  	pgd = pgd_offset(mm, addr);
>  	pr_debug("%s: addr:0x%lx pgd:%p\n", __func__, addr, pgd);
> @@ -217,19 +218,29 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
>  		return NULL;
>  
>  	pud = pud_offset(pgd, addr);
> -	if (pud_none(*pud))
> +	if (pud_none(*pud) && sz != PUD_SIZE)
>  		return NULL;
>  	/* swap or huge page */
>  	if (!pud_present(*pud) || pud_huge(*pud))
>  		return (pte_t *)pud;
>  	/* table; check the next level */

So if sz == PUD_SIZE and we have pud_none(*pud) == true, it returns the
pud. Isn't this different from what you proposed for the generic
huge_pte_offset()? [1]

>  
> +	if (sz == CONT_PMD_SIZE)
> +		addr &= CONT_PMD_MASK;
> +
>  	pmd = pmd_offset(pud, addr);
> -	if (pmd_none(*pmd))
> +	if (pmd_none(*pmd) &&
> +	    !(sz == PMD_SIZE || sz == CONT_PMD_SIZE))
>  		return NULL;

Again, if sz == PMD_SIZE, you no longer return NULL. The generic
proposal in [1] looks like:

	if (pmd_none(*pmd))
		return NULL;

and that's even when sz == PMD_SIZE.

Anyway, I think we need to push for [1] again to be accepted before we
go ahead with these changes.

[1] http://lkml.kernel.org/r/20170725154114.24131-2-punit.agrawal@arm.com

-- 
Catalin

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: Re: [PATCH v6 4/9] arm64: hugetlb: Add break-before-make logic for contiguous entries
References: <20170810170906.30772-1-punit.agrawal@arm.com>
	<20170810170906.30772-5-punit.agrawal@arm.com>
	<20170817180311.uwrz64g3bkwfdkrn@armageddon.cambridge.arm.com>
	<87shgpnp6p.fsf@e105922-lin.cambridge.arm.com>
	<20170818104327.a5yep2p3ntjbffug@armageddon.cambridge.arm.com>
Date: Fri, 18 Aug 2017 13:48:56 +0100
In-Reply-To: <20170818104327.a5yep2p3ntjbffug@armageddon.cambridge.arm.com>
	(Catalin Marinas's message of "Fri, 18 Aug 2017 11:43:28 +0100")
Message-ID: <87o9rdnirr.fsf@e105922-lin.cambridge.arm.com>
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To: Catalin Marinas <catalin.marinas@arm.com>
Cc: mark.rutland@arm.com, David Woods <dwoods@mellanox.com>, Steve Capper <steve.capper@arm.com>, will.deacon@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org

Catalin Marinas <catalin.marinas@arm.com> writes:

> On Fri, Aug 18, 2017 at 11:30:22AM +0100, Punit Agrawal wrote:
>> Catalin Marinas <catalin.marinas@arm.com> writes:
>> 
>> > On Thu, Aug 10, 2017 at 06:09:01PM +0100, Punit Agrawal wrote:
>> >> --- a/arch/arm64/mm/hugetlbpage.c
>> >> +++ b/arch/arm64/mm/hugetlbpage.c
>> >> @@ -68,6 +68,62 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
>> >>  	return CONT_PTES;
>> >>  }
>> >>  
>> >> +/*
>> >> + * Changing some bits of contiguous entries requires us to follow a
>> >> + * Break-Before-Make approach, breaking the whole contiguous set
>> >> + * before we can change any entries. See ARM DDI 0487A.k_iss10775,
>> >> + * "Misprogramming of the Contiguous bit", page D4-1762.
>> >> + *
>> >> + * This helper performs the break step.
>> >> + */
>> >> +static pte_t get_clear_flush(struct mm_struct *mm,
>> >> +			     unsigned long addr,
>> >> +			     pte_t *ptep,
>> >> +			     unsigned long pgsize,
>> >> +			     unsigned long ncontig)
>> >> +{
>> >> +	unsigned long i, saddr = addr;
>> >> +	struct vm_area_struct vma = { .vm_mm = mm };
>> >> +	pte_t orig_pte = huge_ptep_get(ptep);
>> >> +
>> >> +	/*
>> >> +	 * If we already have a faulting entry then we don't need
>> >> +	 * to break before make (there won't be a tlb entry cached).
>> >> +	 */
>> >> +	if (!pte_present(orig_pte))
>> >> +		return orig_pte;
>> >
>> > I first thought we could relax this check to pte_valid() as we don't
>> > care about the PROT_NONE case for hardware page table updates. However,
>> > I realised that we call this where we expect the pte to be entirely
>> > cleared but we simply skip it if !present (e.g. swap entry). Is this
>> > correct?
>> 
>> I've checked back and come to the conclusion that get_clear_flush() will
>> not get called with swap entries.
>> 
>> In the case of huge_ptep_get_and_clear() below, the callers
>> (__unmap_hugepage_range() and hugetlb_change_protection()) check for
>> swap entries before calling. Similarly 
>> 
>> I'll relax the check to pte_valid().
>
> Thanks for checking but I would still keep the semantics of the generic
> huge_ptep_get_and_clear() where the entry is always zeroed. It shouldn't
> have any performance impact since this function won't be called for swap
> entries, but just in case anyone changes the core code later on.

Makes sense. I'll drop the check and unconditionally clear the entries.

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From: Punit Agrawal <punit.agrawal@arm.com>
Subject: Re: [PATCH v6 5/9] arm64: hugetlb: Handle swap entries in huge_pte_offset() for contiguous hugepages
References: <20170810170906.30772-1-punit.agrawal@arm.com>
	<20170810170906.30772-6-punit.agrawal@arm.com>
	<20170818112015.2cvkb7y3gkozz5ip@armageddon.cambridge.arm.com>
Date: Fri, 18 Aug 2017 14:49:41 +0100
In-Reply-To: <20170818112015.2cvkb7y3gkozz5ip@armageddon.cambridge.arm.com>
	(Catalin Marinas's message of "Fri, 18 Aug 2017 12:20:16 +0100")
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To: Catalin Marinas <catalin.marinas@arm.com>
Cc: will.deacon@arm.com, mark.rutland@arm.com, David Woods <dwoods@mellanox.com>, steve.capper@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org

Catalin Marinas <catalin.marinas@arm.com> writes:

> On Thu, Aug 10, 2017 at 06:09:02PM +0100, Punit Agrawal wrote:
>> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
>> index d3a6713048a2..09e79785c019 100644
>> --- a/arch/arm64/mm/hugetlbpage.c
>> +++ b/arch/arm64/mm/hugetlbpage.c
>> @@ -210,6 +210,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
>>  	pgd_t *pgd;
>>  	pud_t *pud;
>>  	pmd_t *pmd;
>> +	pte_t *pte;
>>  
>>  	pgd = pgd_offset(mm, addr);
>>  	pr_debug("%s: addr:0x%lx pgd:%p\n", __func__, addr, pgd);
>> @@ -217,19 +218,29 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
>>  		return NULL;
>>  
>>  	pud = pud_offset(pgd, addr);
>> -	if (pud_none(*pud))
>> +	if (pud_none(*pud) && sz != PUD_SIZE)
>>  		return NULL;
>>  	/* swap or huge page */
>>  	if (!pud_present(*pud) || pud_huge(*pud))
>>  		return (pte_t *)pud;
>>  	/* table; check the next level */
>
> So if sz == PUD_SIZE and we have pud_none(*pud) == true, it returns the
> pud. Isn't this different from what you proposed for the generic
> huge_pte_offset()? [1]

I think I missed this case in the generic version.

As hugetlb_fault() deals with p*d_none() entries by calling
hugetlb_no_page(), the thinking was that returning the p*d saves us an
extra round trip by avoiding the call to huge_pte_alloc().

>
>>  
>> +	if (sz == CONT_PMD_SIZE)
>> +		addr &= CONT_PMD_MASK;
>> +
>>  	pmd = pmd_offset(pud, addr);
>> -	if (pmd_none(*pmd))
>> +	if (pmd_none(*pmd) &&
>> +	    !(sz == PMD_SIZE || sz == CONT_PMD_SIZE))
>>  		return NULL;
>
> Again, if sz == PMD_SIZE, you no longer return NULL. The generic
> proposal in [1] looks like:
>
> 	if (pmd_none(*pmd))
> 		return NULL;
>
> and that's even when sz == PMD_SIZE.
>
> Anyway, I think we need to push for [1] again to be accepted before we
> go ahead with these changes.

[1] is already queued in Andrew's tree. I'll send an update - hopefully
it can be picked up for the next merge.

>
> [1] http://lkml.kernel.org/r/20170725154114.24131-2-punit.agrawal@arm.com

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