x86: mm: avoid allocating struct mm_struct on the stack

struct mm_struct is quite large (~1664 bytes) and so allocating on the
stack may cause problems as the kernel stack size is small.

Since ptdump_walk_pgd_level_core() was only allocating the structure so
that it could modify the pgd argument we can instead introduce a pgd
override in struct mm_walk and pass this down the call stack to where it
is needed.

Since the correct mm_struct is now being passed down, it is now also
unnecessary to take the mmap_sem semaphore because ptdump_walk_pgd() will
now take the semaphore on the real mm.

[steven.price@arm.com: restore missed arm64 changes]
Link: http://lkml.kernel.org/r/20200108145710.34314-1-steven.price@arm.com
Link: http://lkml.kernel.org/r/20200108145710.34314-1-steven.price@arm.com
Signed-off-by: Steven Price <steven.price@arm.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: "Liang, Kan" <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zong Li <zong.li@sifive.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
index ef4b3ca..860c00e 100644 (file)
--- a/arch/arm64/mm/dump.c
+++ b/arch/arm64/mm/dump.c
@@ -323,7 +323,7 @@ void ptdump_walk(struct seq_file *s, struct ptdump_info *info)
                }
        };
 
-       ptdump_walk_pgd(&st.ptdump, info->mm);
+       ptdump_walk_pgd(&st.ptdump, info->mm, NULL);
 }
 
 static void ptdump_initialize(void)
@@ -361,7 +361,7 @@ void ptdump_check_wx(void)
                }
        };
 
-       ptdump_walk_pgd(&st.ptdump, &init_mm);
+       ptdump_walk_pgd(&st.ptdump, &init_mm, NULL);
 
        if (st.wx_pages || st.uxn_pages)
                pr_warn("Checked W+X mappings: FAILED, %lu W+X pages found, %lu non-UXN pages found\n",

diff --git a/arch/x86/mm/debug_pagetables.c b/arch/x86/mm/debug_pagetables.c
index d0efec7..4a3b62f 100644 (file)
--- a/arch/x86/mm/debug_pagetables.c
+++ b/arch/x86/mm/debug_pagetables.c
@@ -15,11 +15,8 @@ DEFINE_SHOW_ATTRIBUTE(ptdump);
 
 static int ptdump_curknl_show(struct seq_file *m, void *v)
 {
-       if (current->mm->pgd) {
-               down_read(&current->mm->mmap_sem);
+       if (current->mm->pgd)
                ptdump_walk_pgd_level_debugfs(m, current->mm, false);
-               up_read(&current->mm->mmap_sem);
-       }
        return 0;
 }
 
@@ -28,11 +25,8 @@ DEFINE_SHOW_ATTRIBUTE(ptdump_curknl);
 #ifdef CONFIG_PAGE_TABLE_ISOLATION
 static int ptdump_curusr_show(struct seq_file *m, void *v)
 {
-       if (current->mm->pgd) {
-               down_read(&current->mm->mmap_sem);
+       if (current->mm->pgd)
                ptdump_walk_pgd_level_debugfs(m, current->mm, true);
-               up_read(&current->mm->mmap_sem);
-       }
        return 0;
 }
 

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 411f6a7..64229da 100644 (file)
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -357,7 +357,8 @@ static void note_page(struct ptdump_state *pt_st, unsigned long addr, int level,
        }
 }
 
-static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
+static void ptdump_walk_pgd_level_core(struct seq_file *m,
+                                      struct mm_struct *mm, pgd_t *pgd,
                                       bool checkwx, bool dmesg)
 {
        const struct ptdump_range ptdump_ranges[] = {
@@ -386,12 +387,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
                .seq            = m
        };
 
-       struct mm_struct fake_mm = {
-               .pgd = pgd
-       };
-       init_rwsem(&fake_mm.mmap_sem);
-
-       ptdump_walk_pgd(&st.ptdump, &fake_mm);
+       ptdump_walk_pgd(&st.ptdump, mm, pgd);
 
        if (!checkwx)
                return;
@@ -404,7 +400,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
 
 void ptdump_walk_pgd_level(struct seq_file *m, struct mm_struct *mm)
 {
-       ptdump_walk_pgd_level_core(m, mm->pgd, false, true);
+       ptdump_walk_pgd_level_core(m, mm, mm->pgd, false, true);
 }
 
 void ptdump_walk_pgd_level_debugfs(struct seq_file *m, struct mm_struct *mm,
@@ -415,7 +411,7 @@ void ptdump_walk_pgd_level_debugfs(struct seq_file *m, struct mm_struct *mm,
        if (user && boot_cpu_has(X86_FEATURE_PTI))
                pgd = kernel_to_user_pgdp(pgd);
 #endif
-       ptdump_walk_pgd_level_core(m, pgd, false, false);
+       ptdump_walk_pgd_level_core(m, mm, pgd, false, false);
 }
 EXPORT_SYMBOL_GPL(ptdump_walk_pgd_level_debugfs);
 
@@ -430,13 +426,13 @@ void ptdump_walk_user_pgd_level_checkwx(void)
 
        pr_info("x86/mm: Checking user space page tables\n");
        pgd = kernel_to_user_pgdp(pgd);
-       ptdump_walk_pgd_level_core(NULL, pgd, true, false);
+       ptdump_walk_pgd_level_core(NULL, &init_mm, pgd, true, false);
 #endif
 }
 
 void ptdump_walk_pgd_level_checkwx(void)
 {
-       ptdump_walk_pgd_level_core(NULL, INIT_PGD, true, false);
+       ptdump_walk_pgd_level_core(NULL, &init_mm, INIT_PGD, true, false);
 }
 
 static int __init pt_dump_init(void)

diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
index 745a654..b1cb6b7 100644 (file)
--- a/include/linux/pagewalk.h
+++ b/include/linux/pagewalk.h
@@ -74,6 +74,7 @@ enum page_walk_action {
  * mm_walk - walk_page_range data
  * @ops:       operation to call during the walk
  * @mm:                mm_struct representing the target process of page table walk
+ * @pgd:       pointer to PGD; only valid with no_vma (otherwise set to NULL)
  * @vma:       vma currently walked (NULL if walking outside vmas)
  * @action:    next action to perform (see enum page_walk_action)
  * @no_vma:    walk ignoring vmas (vma will always be NULL)
@@ -84,6 +85,7 @@ enum page_walk_action {
 struct mm_walk {
        const struct mm_walk_ops *ops;
        struct mm_struct *mm;
+       pgd_t *pgd;
        struct vm_area_struct *vma;
        enum page_walk_action action;
        bool no_vma;
@@ -95,6 +97,7 @@ int walk_page_range(struct mm_struct *mm, unsigned long start,
                void *private);
 int walk_page_range_novma(struct mm_struct *mm, unsigned long start,
                          unsigned long end, const struct mm_walk_ops *ops,
+                         pgd_t *pgd,
                          void *private);
 int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
                void *private);

diff --git a/include/linux/ptdump.h b/include/linux/ptdump.h
index b28f3f2..a67065c 100644 (file)
--- a/include/linux/ptdump.h
+++ b/include/linux/ptdump.h
@@ -17,6 +17,6 @@ struct ptdump_state {
        const struct ptdump_range *range;
 };
 
-void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm);
+void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd);
 
 #endif /* _LINUX_PTDUMP_H */

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 5895ce4..928df16 100644 (file)
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -206,7 +206,10 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
        const struct mm_walk_ops *ops = walk->ops;
        int err = 0;
 
-       pgd = pgd_offset(walk->mm, addr);
+       if (walk->pgd)
+               pgd = walk->pgd + pgd_index(addr);
+       else
+               pgd = pgd_offset(walk->mm, addr);
        do {
                next = pgd_addr_end(addr, end);
                if (pgd_none_or_clear_bad(pgd)) {
@@ -436,11 +439,13 @@ int walk_page_range(struct mm_struct *mm, unsigned long start,
  */
 int walk_page_range_novma(struct mm_struct *mm, unsigned long start,
                          unsigned long end, const struct mm_walk_ops *ops,
+                         pgd_t *pgd,
                          void *private)
 {
        struct mm_walk walk = {
                .ops            = ops,
                .mm             = mm,
+               .pgd            = pgd,
                .private        = private,
                .no_vma         = true
        };

diff --git a/mm/ptdump.c b/mm/ptdump.c
index ad18a98..26208d0 100644 (file)
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -122,14 +122,14 @@ static const struct mm_walk_ops ptdump_ops = {
        .pte_hole       = ptdump_hole,
 };
 
-void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm)
+void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
 {
        const struct ptdump_range *range = st->range;
 
        down_read(&mm->mmap_sem);
        while (range->start != range->end) {
                walk_page_range_novma(mm, range->start, range->end,
-                                     &ptdump_ops, st);
+                                     &ptdump_ops, pgd, st);
                range++;
        }
        up_read(&mm->mmap_sem);