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>

2 files changed, 4 insertions, 1 deletions

diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
index 745a654c6ea7..b1cb6b753abb 100644
--- 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 b28f3f2acf90..a67065c403c3 100644
--- 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 */