Re: [PATCH 12/19] mm: Define MAP_SYNC and VM_SYNC flags

[Jan Kara <jack@suse.cz>]

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On Fri 13-10-17 13:44:44, Ross Zwisler wrote:
> On Wed, Oct 11, 2017 at 10:05:56PM +0200, Jan Kara wrote:
> > Define new MAP_SYNC flag and corresponding VMA VM_SYNC flag. As the
> > MAP_SYNC flag is not part of LEGACY_MAP_MASK, currently it will be
> > refused by all MAP_SHARED_VALIDATE map attempts and silently ignored for
> > everything else.
> > 
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> >  arch/xtensa/include/uapi/asm/mman.h | 1 +
> >  fs/proc/task_mmu.c                  | 1 +
> >  include/linux/mm.h                  | 1 +
> >  include/linux/mman.h                | 3 ++-
> >  include/uapi/asm-generic/mman.h     | 1 +
> >  5 files changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
> > index ec597900eec7..b62a7ce166fb 100644
> > --- a/arch/xtensa/include/uapi/asm/mman.h
> > +++ b/arch/xtensa/include/uapi/asm/mman.h
> > @@ -56,6 +56,7 @@
> >  #define MAP_NONBLOCK	0x20000		/* do not block on IO */
> >  #define MAP_STACK	0x40000		/* give out an address that is best suited for process/thread stacks */
> >  #define MAP_HUGETLB	0x80000		/* create a huge page mapping */
> > +#define MAP_SYNC	0x100000	/* perform synchronous page faults for the mapping */
> 
> Why define MAP_SYNC for this one architecture, but not for the rest that have
> their own arch/*/include/uapi/asm/mman.h?  AFAIK xtensa doesn't support DAX,
> so has no need for MAP_SYNC?

Yeah, good point. I guess I'll just define it in asm-generic (which covers
x86 as well) and just define MAP_SYNC to 0 if not defined in linux/mman.h.
That should make the code compile and make sure userspace gets error if he
tries to use MAP_SYNC somehow on arch without its definition. Attached is a
new version of the patch.

> Other than this one question, this patch looks fine:
> 
> Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>

Thanks.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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>From e15030463a8be760e10843fc9cf08c082a783c22 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Thu, 17 Aug 2017 11:55:26 +0200
Subject: [PATCH] mm: Define MAP_SYNC and VM_SYNC flags

Define new MAP_SYNC flag and corresponding VMA VM_SYNC flag. As the
MAP_SYNC flag is not part of LEGACY_MAP_MASK, currently it will be
refused by all MAP_SHARED_VALIDATE map attempts and silently ignored for
everything else.

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/proc/task_mmu.c              | 1 +
 include/linux/mm.h              | 1 +
 include/linux/mman.h            | 8 ++++++--
 include/uapi/asm-generic/mman.h | 1 +
 4 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 5589b4bd4b85..ea78b37deeaa 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -664,6 +664,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 		[ilog2(VM_ACCOUNT)]	= "ac",
 		[ilog2(VM_NORESERVE)]	= "nr",
 		[ilog2(VM_HUGETLB)]	= "ht",
+		[ilog2(VM_SYNC)]	= "sf",
 		[ilog2(VM_ARCH_1)]	= "ar",
 		[ilog2(VM_WIPEONFORK)]	= "wf",
 		[ilog2(VM_DONTDUMP)]	= "dd",
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 55a9d2d109d9..cb62f2127314 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -189,6 +189,7 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_ACCOUNT	0x00100000	/* Is a VM accounted object */
 #define VM_NORESERVE	0x00200000	/* should the VM suppress accounting */
 #define VM_HUGETLB	0x00400000	/* Huge TLB Page VM */
+#define VM_SYNC		0x00800000	/* Synchronous page faults */
 #define VM_ARCH_1	0x01000000	/* Architecture-specific flag */
 #define VM_WIPEONFORK	0x02000000	/* Wipe VMA contents in child. */
 #define VM_DONTDUMP	0x04000000	/* Do not include in the core dump */
diff --git a/include/linux/mman.h b/include/linux/mman.h
index 94b63b4d71ff..8f7cc87828e6 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -9,7 +9,7 @@
 
 /*
  * Arrange for legacy / undefined architecture specific flags to be
- * ignored by default in LEGACY_MAP_MASK.
+ * ignored by mmap handling code.
  */
 #ifndef MAP_32BIT
 #define MAP_32BIT 0
@@ -23,6 +23,9 @@
 #ifndef MAP_UNINITIALIZED
 #define MAP_UNINITIALIZED 0
 #endif
+#ifndef MAP_SYNC
+#define MAP_SYNC 0
+#endif
 
 /*
  * The historical set of flags that all mmap implementations implicitly
@@ -125,7 +128,8 @@ calc_vm_flag_bits(unsigned long flags)
 {
 	return _calc_vm_trans(flags, MAP_GROWSDOWN,  VM_GROWSDOWN ) |
 	       _calc_vm_trans(flags, MAP_DENYWRITE,  VM_DENYWRITE ) |
-	       _calc_vm_trans(flags, MAP_LOCKED,     VM_LOCKED    );
+	       _calc_vm_trans(flags, MAP_LOCKED,     VM_LOCKED    ) |
+	       _calc_vm_trans(flags, MAP_SYNC,	     VM_SYNC      );
 }
 
 unsigned long vm_commit_limit(void);
diff --git a/include/uapi/asm-generic/mman.h b/include/uapi/asm-generic/mman.h
index 7162cd4cca73..00e55627d2df 100644
--- a/include/uapi/asm-generic/mman.h
+++ b/include/uapi/asm-generic/mman.h
@@ -12,6 +12,7 @@
 #define MAP_NONBLOCK	0x10000		/* do not block on IO */
 #define MAP_STACK	0x20000		/* give out an address that is best suited for process/thread stacks */
 #define MAP_HUGETLB	0x40000		/* create a huge page mapping */
+#define MAP_SYNC	0x80000		/* perform synchronous page faults for the mapping */
 
 /* Bits [26:31] are reserved, see mman-common.h for MAP_HUGETLB usage */
 
-- 
2.12.3