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selftests/vm: anon_cow: add mprotect() optimization tests 

Let's extend the test to cover the possible mprotect() optimization when
removing write-protection. mprotect() must not allow write-access to a
COW-shared page by accident.

Link: https://lkml.kernel.org/r/20221108174652.198904-8-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2022-11-08 18:46:52 +01:00 committed by Andrew Morton
parent d6379159f4
commit 07f8bac498
1 changed files with 46 additions and 3 deletions
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49
tools/testing/selftests/vm/anon_cow.c
View File

@ -190,7 +190,8 @@ static int child_vmsplice_memcmp_fn(char *mem, size_t size,
typedef int (*child_fn)(char *mem, size_t size, struct comm_pipes *comm_pipes);
static void do_test_cow_in_parent(char *mem, size_t size, child_fn fn)
static void do_test_cow_in_parent(char *mem, size_t size, bool do_mprotect,
child_fn fn)
{
struct comm_pipes comm_pipes;
char buf;
@ -212,6 +213,22 @@ static void do_test_cow_in_parent(char *mem, size_t size, child_fn fn)
while (read(comm_pipes.child_ready[0], &buf, 1) != 1)
;
if (do_mprotect) {
/*
* mprotect() optimizations might try avoiding
* write-faults by directly mapping pages writable.
*/
ret = mprotect(mem, size, PROT_READ);
ret |= mprotect(mem, size, PROT_READ|PROT_WRITE);
if (ret) {
ksft_test_result_fail("mprotect() failed\n");
write(comm_pipes.parent_ready[1], "0", 1);
wait(&ret);
goto close_comm_pipes;
}
}
/* Modify the page. */
memset(mem, 0xff, size);
write(comm_pipes.parent_ready[1], "0", 1);
@ -229,12 +246,22 @@ close_comm_pipes:
static void test_cow_in_parent(char *mem, size_t size)
{
do_test_cow_in_parent(mem, size, child_memcmp_fn);
do_test_cow_in_parent(mem, size, false, child_memcmp_fn);
}
static void test_cow_in_parent_mprotect(char *mem, size_t size)
{
do_test_cow_in_parent(mem, size, true, child_memcmp_fn);
}
static void test_vmsplice_in_child(char *mem, size_t size)
{
do_test_cow_in_parent(mem, size, child_vmsplice_memcmp_fn);
do_test_cow_in_parent(mem, size, false, child_vmsplice_memcmp_fn);
}
static void test_vmsplice_in_child_mprotect(char *mem, size_t size)
{
do_test_cow_in_parent(mem, size, true, child_vmsplice_memcmp_fn);
}
static void do_test_vmsplice_in_parent(char *mem, size_t size,
@ -969,6 +996,14 @@ static const struct test_case test_cases[] = {
"Basic COW after fork()",
test_cow_in_parent,
},
/*
* Basic test, but do an additional mprotect(PROT_READ)+
* mprotect(PROT_READ|PROT_WRITE) in the parent before write access.
*/
{
"Basic COW after fork() with mprotect() optimization",
test_cow_in_parent_mprotect,
},
/*
* vmsplice() [R/O GUP] + unmap in the child; modify in the parent. If
* we miss to break COW, the child observes modifications by the parent.
@ -978,6 +1013,14 @@ static const struct test_case test_cases[] = {
"vmsplice() + unmap in child",
test_vmsplice_in_child
},
/*
* vmsplice() test, but do an additional mprotect(PROT_READ)+
* mprotect(PROT_READ|PROT_WRITE) in the parent before write access.
*/
{
"vmsplice() + unmap in child with mprotect() optimization",
test_vmsplice_in_child_mprotect
},
/*
* vmsplice() [R/O GUP] in parent before fork(), unmap in parent after
* fork(); modify in the child. If we miss to break COW, the parent