linux-kernel - [PATCH v13 13/22] mm: pagewalk: Add test

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Date:   Thu, 24 Oct 2019 10:37:07 +0100
From:   Steven Price <steven.price@....com>
To:     linux-mm@...ck.org
Cc:     Steven Price <steven.price@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        James Morse <james.morse@....com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Mark Rutland <Mark.Rutland@....com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH v13 13/22] mm: pagewalk: Add test_p?d callbacks

It is useful to be able to skip parts of the page table tree even when
walking without VMAs. Add test_p?d callbacks similar to test_walk but
which are called just before a table at that level is walked. If the
callback returns non-zero then the entire table is skipped.

Signed-off-by: Steven Price <steven.price@....com>
---
 include/linux/pagewalk.h | 11 +++++++++++
 mm/pagewalk.c            | 24 ++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
index 12004b097eae..df424197a25a 100644
--- a/include/linux/pagewalk.h
+++ b/include/linux/pagewalk.h
@@ -24,6 +24,11 @@ struct mm_walk;
  *			"do page table walk over the current vma", returning
  *			a negative value means "abort current page table walk
  *			right now" and returning 1 means "skip the current vma"
+ * @test_pmd:		similar to test_walk(), but called for every pmd.
+ * @test_pud:		similar to test_walk(), but called for every pud.
+ * @test_p4d:		similar to test_walk(), but called for every p4d.
+ *			Returning 0 means walk this part of the page tables,
+ *			returning 1 means to skip this range.
  *
  * p?d_entry callbacks are called even if those levels are folded on a
  * particular architecture/configuration.
@@ -46,6 +51,12 @@ struct mm_walk_ops {
 			     struct mm_walk *walk);
 	int (*test_walk)(unsigned long addr, unsigned long next,
 			struct mm_walk *walk);
+	int (*test_pmd)(unsigned long addr, unsigned long next,
+			pmd_t *pmd_start, struct mm_walk *walk);
+	int (*test_pud)(unsigned long addr, unsigned long next,
+			pud_t *pud_start, struct mm_walk *walk);
+	int (*test_p4d)(unsigned long addr, unsigned long next,
+			p4d_t *p4d_start, struct mm_walk *walk);
 };
 
 /**
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 4139e9163aee..43acffefd43f 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -34,6 +34,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
 	const struct mm_walk_ops *ops = walk->ops;
 	int err = 0;
 
+	if (ops->test_pmd) {
+		err = ops->test_pmd(addr, end, pmd_offset(pud, 0UL), walk);
+		if (err < 0)
+			return err;
+		if (err > 0)
+			return 0;
+	}
+
 	pmd = pmd_offset(pud, addr);
 	do {
 again:
@@ -85,6 +93,14 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
 	const struct mm_walk_ops *ops = walk->ops;
 	int err = 0;
 
+	if (ops->test_pud) {
+		err = ops->test_pud(addr, end, pud_offset(p4d, 0UL), walk);
+		if (err < 0)
+			return err;
+		if (err > 0)
+			return 0;
+	}
+
 	pud = pud_offset(p4d, addr);
 	do {
  again:
@@ -128,6 +144,14 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
 	const struct mm_walk_ops *ops = walk->ops;
 	int err = 0;
 
+	if (ops->test_p4d) {
+		err = ops->test_p4d(addr, end, p4d_offset(pgd, 0UL), walk);
+		if (err < 0)
+			return err;
+		if (err > 0)
+			return 0;
+	}
+
 	p4d = p4d_offset(pgd, addr);
 	do {
 		next = p4d_addr_end(addr, end);
-- 
2.20.1