2022-04-27 08:56:25

by liusongtang

[permalink] [raw]
Subject: [PATCH] mm/mprotect: reduce Committed_AS if memory protection is changed to PROT_NONE

If PROT_WRITE is set, the size of vm area will be added to Committed_AS.
However, if memory protection is changed to PROT_NONE,
the corresponding physical memory will not be used, but Committed_AS still
count the size of the PROT_NONE memory.

This patch reduce Committed_AS and free the corresponding memory if
memory protection is changed to PROT_NONE.

Signed-off-by: liusongtang <[email protected]>
---
mm/mprotect.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index b69ce7a..c3121e6 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -497,6 +497,12 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
}

success:
+ if ((newflags & (VM_READ | VM_WRITE | VM_EXEC | VM_LOCKED | VM_ACCOUNT)) == VM_ACCOUNT) {
+ zap_page_range(vma, start, end - start);
+ newflags &= ~VM_ACCOUNT;
+ vm_unacct_memory((end - start) >> PAGE_SHIFT);
+ }
+
/*
* vm_flags and vm_page_prot are protected by the mmap_lock
* held in write mode.
--
2.12.3


2022-04-27 09:41:43

by Andrew Morton

[permalink] [raw]
Subject: Re: [PATCH] mm/mprotect: reduce Committed_AS if memory protection is changed to PROT_NONE

On Tue, 26 Apr 2022 19:27:05 +0800 liusongtang <[email protected]> wrote:

> If PROT_WRITE is set, the size of vm area will be added to Committed_AS.
> However, if memory protection is changed to PROT_NONE,
> the corresponding physical memory will not be used, but Committed_AS still
> count the size of the PROT_NONE memory.
>
> This patch reduce Committed_AS and free the corresponding memory if
> memory protection is changed to PROT_NONE.
>
> ...
>
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -497,6 +497,12 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
> }
>
> success:
> + if ((newflags & (VM_READ | VM_WRITE | VM_EXEC | VM_LOCKED | VM_ACCOUNT)) == VM_ACCOUNT) {
> + zap_page_range(vma, start, end - start);
> + newflags &= ~VM_ACCOUNT;
> + vm_unacct_memory((end - start) >> PAGE_SHIFT);
> + }
> +
> /*
> * vm_flags and vm_page_prot are protected by the mmap_lock
> * held in write mode.

Surprised. If userspace does mprotect(addr, len. PROT_NONE) then
mprotect(addr, len. PROT_READ), what is now at *addr? Zeroes?

2022-05-03 01:31:06

by kernel test robot

[permalink] [raw]
Subject: [mm/mprotect] 5e1e18b334: kvm-unit-tests.eventinj.fail



Greeting,

FYI, we noticed the following commit (built with gcc-11):

commit: 5e1e18b33470f3b7cff87166b39fc068333ec8be ("[PATCH] mm/mprotect: reduce Committed_AS if memory protection is changed to PROT_NONE")
url: https://github.com/intel-lab-lkp/linux/commits/liusongtang/mm-mprotect-reduce-Committed_AS-if-memory-protection-is-changed-to-PROT_NONE/20220426-192805
base: https://github.com/hnaz/linux-mm master
patch link: https://lore.kernel.org/linux-mm/[email protected]

in testcase: kvm-unit-tests
version: kvm-unit-tests-x86_64-1a4529c-1_20220412
with following parameters:

ucode: 0x28



on test machine: 8 threads 1 sockets Intel(R) Core(TM) i7-4790 v3 @ 3.60GHz with 6G memory

caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):




If you fix the issue, kindly add following tag
Reported-by: kernel test robot <[email protected]>



SKIP asyncpf (0 tests)
PASS emulator (141 tests, 1 skipped)
FAIL eventinj
PASS hypercall (2 tests)
PASS idt_test (4 tests)



To reproduce:

git clone https://github.com/intel/lkp-tests.git
cd lkp-tests
sudo bin/lkp install job.yaml # job file is attached in this email
bin/lkp split-job --compatible job.yaml # generate the yaml file for lkp run
sudo bin/lkp run generated-yaml-file

# if come across any failure that blocks the test,
# please remove ~/.lkp and /lkp dir to run from a clean state.



--
0-DAY CI Kernel Test Service
https://01.org/lkp



Attachments:
(No filename) (1.60 kB)
config-5.18.0-rc4-mm1-00335-g5e1e18b33470 (169.11 kB)
job-script (5.67 kB)
dmesg.xz (18.09 kB)
kvm-unit-tests (2.88 kB)
job.yaml (4.60 kB)
reproduce (16.00 B)
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