MPX-enabled application will possibly create a lot of bounds tables
in process address space to save bounds information. These tables
can take up huge swaths of memory (as much as 80% of the memory on
the system) even if we clean them up aggressively. Being this huge,
we need a way to track their memory use. If we want to track them,
we essentially have two options:
1. walk the multi-GB (in virtual space) bounds directory to locate
all the VMAs and walk them
2. Find a way to distinguish MPX bounds-table VMAs from normal
anonymous VMAs and use some existing mechanism to walk them
We expect (1) will be prohibitively expensive. For (2), we only
need a single bit, and we've chosen to use a VM_ flag. We understand
that they are scarce and are open to other options.
There is one potential hybrid approach: check the bounds directory
entry for any anonymous VMA that could possibly contain a bounds table.
This is less expensive than (1), but still requires reading a pointer
out of userspace for every VMA that we iterate over.
Signed-off-by: Qiaowei Ren <qiaowei....@intel.com>
---
fs/proc/task_mmu.c | 1 +
include/linux/mm.h | 2 ++
2 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index cfa63ee..b2bc755 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -549,6 +549,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct
vm_area_struct *vma)
[ilog2(VM_GROWSDOWN)] = "gd",
[ilog2(VM_PFNMAP)] = "pf",
[ilog2(VM_DENYWRITE)] = "dw",
+ [ilog2(VM_MPX)] = "mp",
[ilog2(VM_LOCKED)] = "lo",
[ilog2(VM_IO)] = "io",
[ilog2(VM_SEQ_READ)] = "sr",
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e03dd29..44c75d7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -127,6 +127,8 @@ extern unsigned int kobjsize(const void *objp);
#define VM_HUGETLB 0x00400000 /* Huge TLB Page VM */
#define VM_NONLINEAR 0x00800000 /* Is non-linear (remap_file_pages) */
#define VM_ARCH_1 0x01000000 /* Architecture-specific flag */
+/* MPX specific bounds table or bounds directory (x86) */
+#define VM_MPX 0x02000000
#define VM_DONTDUMP 0x04000000 /* Do not include in the core dump */
#ifdef CONFIG_MEM_SOFT_DIRTY
--
1.7.1
--
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