Let's test some basic functionality using /dev/mem. These tests will implicitly cover some PAT (Page Attribute Handling) handling on x86.
These tests will only run when /dev/mem access to the first two pages in physical address space is possible and allowed; otherwise, the tests are skipped.
On current x86-64 with PAT inside a VM, all tests pass:
TAP version 13 1..6 # Starting 6 tests from 1 test cases. # RUN pfnmap.madvise_disallowed ... # OK pfnmap.madvise_disallowed ok 1 pfnmap.madvise_disallowed # RUN pfnmap.munmap_split ... # OK pfnmap.munmap_split ok 2 pfnmap.munmap_split # RUN pfnmap.mremap_fixed ... # OK pfnmap.mremap_fixed ok 3 pfnmap.mremap_fixed # RUN pfnmap.mremap_shrink ... # OK pfnmap.mremap_shrink ok 4 pfnmap.mremap_shrink # RUN pfnmap.mremap_expand ... # OK pfnmap.mremap_expand ok 5 pfnmap.mremap_expand # RUN pfnmap.fork ... # OK pfnmap.fork ok 6 pfnmap.fork # PASSED: 6 / 6 tests passed. # Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0
However, we are able to trigger:
[ 27.888251] x86/PAT: pfnmap:1790 freeing invalid memtype [mem 0x00000000-0x00000fff]
There are probably more things worth testing in the future, such as MAP_PRIVATE handling. But this set of tests is sufficient to cover most of the things we will rework regarding PAT handling.
Cc: Andrew Morton akpm@linux-foundation.org Cc: Shuah Khan shuah@kernel.org Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Ingo Molnar mingo@redhat.com Cc: Peter Xu peterx@redhat.com Cc: Dev Jain dev.jain@arm.com Signed-off-by: David Hildenbrand david@redhat.com ---
Hopefully I didn't miss any review feedback.
v1 -> v2: * Rewrite using kselftest_harness, which simplifies a lot of things * Add to .gitignore and run_vmtests.sh * Register signal handler on demand * Use volatile trick to force a read (not factoring out FORCE_READ just yet) * Drop mprotect() test case * Add some more comments why we test certain things * Use NULL for mmap() first parameter instead of 0 * Smaller fixes
--- tools/testing/selftests/mm/.gitignore | 1 + tools/testing/selftests/mm/Makefile | 1 + tools/testing/selftests/mm/pfnmap.c | 196 ++++++++++++++++++++++ tools/testing/selftests/mm/run_vmtests.sh | 4 + 4 files changed, 202 insertions(+) create mode 100644 tools/testing/selftests/mm/pfnmap.c
diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore index 91db34941a143..824266982aa36 100644 --- a/tools/testing/selftests/mm/.gitignore +++ b/tools/testing/selftests/mm/.gitignore @@ -20,6 +20,7 @@ mremap_test on-fault-limit transhuge-stress pagemap_ioctl +pfnmap *.tmp* protection_keys protection_keys_32 diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile index ad4d6043a60f0..ae6f994d3add7 100644 --- a/tools/testing/selftests/mm/Makefile +++ b/tools/testing/selftests/mm/Makefile @@ -84,6 +84,7 @@ TEST_GEN_FILES += mremap_test TEST_GEN_FILES += mseal_test TEST_GEN_FILES += on-fault-limit TEST_GEN_FILES += pagemap_ioctl +TEST_GEN_FILES += pfnmap TEST_GEN_FILES += thuge-gen TEST_GEN_FILES += transhuge-stress TEST_GEN_FILES += uffd-stress diff --git a/tools/testing/selftests/mm/pfnmap.c b/tools/testing/selftests/mm/pfnmap.c new file mode 100644 index 0000000000000..8a9d19b6020c7 --- /dev/null +++ b/tools/testing/selftests/mm/pfnmap.c @@ -0,0 +1,196 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Basic VM_PFNMAP tests relying on mmap() of '/dev/mem' + * + * Copyright 2025, Red Hat, Inc. + * + * Author(s): David Hildenbrand david@redhat.com + */ +#define _GNU_SOURCE +#include <stdlib.h> +#include <string.h> +#include <stdint.h> +#include <unistd.h> +#include <errno.h> +#include <fcntl.h> +#include <signal.h> +#include <setjmp.h> +#include <linux/mman.h> +#include <sys/mman.h> +#include <sys/wait.h> + +#include "../kselftest_harness.h" +#include "vm_util.h" + +static sigjmp_buf sigjmp_buf_env; + +static void signal_handler(int sig) +{ + siglongjmp(sigjmp_buf_env, -EFAULT); +} + +static int test_read_access(char *addr, size_t size, size_t pagesize) +{ + size_t offs; + int ret; + + if (signal(SIGSEGV, signal_handler) == SIG_ERR) + return -EINVAL; + + ret = sigsetjmp(sigjmp_buf_env, 1); + if (!ret) { + for (offs = 0; offs < size; offs += pagesize) + /* Force a read that the compiler cannot optimize out. */ + *((volatile char *)(addr + offs)); + } + if (signal(SIGSEGV, signal_handler) == SIG_ERR) + return -EINVAL; + + return ret; +} + +FIXTURE(pfnmap) +{ + size_t pagesize; + int dev_mem_fd; + char *addr1; + size_t size1; + char *addr2; + size_t size2; +}; + +FIXTURE_SETUP(pfnmap) +{ + self->pagesize = getpagesize(); + + self->dev_mem_fd = open("/dev/mem", O_RDONLY); + if (self->dev_mem_fd < 0) + SKIP(return, "Cannot open '/dev/mem'\n"); + + /* We'll require the first two pages throughout our tests ... */ + self->size1 = self->pagesize * 2; + self->addr1 = mmap(NULL, self->size1, PROT_READ, MAP_SHARED, + self->dev_mem_fd, 0); + if (self->addr1 == MAP_FAILED) + SKIP(return, "Cannot mmap '/dev/mem'\n"); + + /* ... and want to be able to read from them. */ + if (test_read_access(self->addr1, self->size1, self->pagesize)) + SKIP(return, "Cannot read-access mmap'ed '/dev/mem'\n"); + + self->size2 = 0; + self->addr2 = MAP_FAILED; +} + +FIXTURE_TEARDOWN(pfnmap) +{ + if (self->addr2 != MAP_FAILED) + munmap(self->addr2, self->size2); + if (self->addr1 != MAP_FAILED) + munmap(self->addr1, self->size1); + if (self->dev_mem_fd >= 0) + close(self->dev_mem_fd); +} + +TEST_F(pfnmap, madvise_disallowed) +{ + int advices[] = { + MADV_DONTNEED, + MADV_DONTNEED_LOCKED, + MADV_FREE, + MADV_WIPEONFORK, + MADV_COLD, + MADV_PAGEOUT, + MADV_POPULATE_READ, + MADV_POPULATE_WRITE, + }; + int i; + + /* All these advices must be rejected. */ + for (i = 0; i < ARRAY_SIZE(advices); i++) { + EXPECT_LT(madvise(self->addr1, self->pagesize, advices[i]), 0); + EXPECT_EQ(errno, EINVAL); + } +} + +TEST_F(pfnmap, munmap_split) +{ + /* + * Unmap the first page. This munmap() call is not really expected to + * fail, but we might be able to trigger other internal issues. + */ + ASSERT_EQ(munmap(self->addr1, self->pagesize), 0); + + /* + * Remap the first page while the second page is still mapped. This + * makes sure that any PAT tracking on x86 will allow for mmap()'ing + * a page again while some parts of the first mmap() are still + * around. + */ + self->size2 = self->pagesize; + self->addr2 = mmap(NULL, self->pagesize, PROT_READ, MAP_SHARED, + self->dev_mem_fd, 0); + ASSERT_NE(self->addr2, MAP_FAILED); +} + +TEST_F(pfnmap, mremap_fixed) +{ + char *ret; + + /* Reserve a destination area. */ + self->size2 = self->size1; + self->addr2 = mmap(NULL, self->size2, PROT_READ, MAP_ANON | MAP_PRIVATE, + -1, 0); + ASSERT_NE(self->addr2, MAP_FAILED); + + /* mremap() over our destination. */ + ret = mremap(self->addr1, self->size1, self->size2, + MREMAP_FIXED | MREMAP_MAYMOVE, self->addr2); + ASSERT_NE(ret, MAP_FAILED); +} + +TEST_F(pfnmap, mremap_shrink) +{ + char *ret; + + /* Shrinking is expected to work. */ + ret = mremap(self->addr1, self->size1, self->size1 - self->pagesize, 0); + ASSERT_NE(ret, MAP_FAILED); +} + +TEST_F(pfnmap, mremap_expand) +{ + /* + * Growing is not expected to work, and getting it right would + * be challenging. So this test primarily serves as an early warning + * that something that probably should never work suddenly works. + */ + self->size2 = self->size1 + self->pagesize; + self->addr2 = mremap(self->addr1, self->size1, self->size2, MREMAP_MAYMOVE); + ASSERT_EQ(self->addr2, MAP_FAILED); +} + +TEST_F(pfnmap, fork) +{ + pid_t pid; + int ret; + + /* fork() a child and test if the child can access the pages. */ + pid = fork(); + ASSERT_GE(pid, 0); + + if (!pid) { + EXPECT_EQ(test_read_access(self->addr1, self->size1, + self->pagesize), 0); + exit(0); + } + + wait(&ret); + if (WIFEXITED(ret)) + ret = WEXITSTATUS(ret); + else + ret = -EINVAL; + ASSERT_EQ(ret, 0); +} + +TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh index 188b125bf1f6b..dddd1dd8af145 100755 --- a/tools/testing/selftests/mm/run_vmtests.sh +++ b/tools/testing/selftests/mm/run_vmtests.sh @@ -63,6 +63,8 @@ separated by spaces: test soft dirty page bit semantics - pagemap test pagemap_scan IOCTL +- pfnmap + tests for VM_PFNMAP handling - cow test copy-on-write semantics - thp @@ -472,6 +474,8 @@ fi
CATEGORY="pagemap" run_test ./pagemap_ioctl
+CATEGORY="pfnmap" run_test ./pfnmap + # COW tests CATEGORY="cow" run_test ./cow
On Fri, May 09, 2025 at 05:30:32PM +0200, David Hildenbrand wrote:
Let's test some basic functionality using /dev/mem. These tests will implicitly cover some PAT (Page Attribute Handling) handling on x86.
These tests will only run when /dev/mem access to the first two pages in physical address space is possible and allowed; otherwise, the tests are skipped.
On current x86-64 with PAT inside a VM, all tests pass:
TAP version 13 1..6 # Starting 6 tests from 1 test cases. # RUN pfnmap.madvise_disallowed ... # OK pfnmap.madvise_disallowed ok 1 pfnmap.madvise_disallowed # RUN pfnmap.munmap_split ... # OK pfnmap.munmap_split ok 2 pfnmap.munmap_split # RUN pfnmap.mremap_fixed ... # OK pfnmap.mremap_fixed ok 3 pfnmap.mremap_fixed # RUN pfnmap.mremap_shrink ... # OK pfnmap.mremap_shrink ok 4 pfnmap.mremap_shrink # RUN pfnmap.mremap_expand ... # OK pfnmap.mremap_expand ok 5 pfnmap.mremap_expand # RUN pfnmap.fork ... # OK pfnmap.fork ok 6 pfnmap.fork # PASSED: 6 / 6 tests passed. # Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0
However, we are able to trigger:
[ 27.888251] x86/PAT: pfnmap:1790 freeing invalid memtype [mem 0x00000000-0x00000fff]
There are probably more things worth testing in the future, such as MAP_PRIVATE handling. But this set of tests is sufficient to cover most of the things we will rework regarding PAT handling.
Cc: Andrew Morton akpm@linux-foundation.org Cc: Shuah Khan shuah@kernel.org Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Ingo Molnar mingo@redhat.com Cc: Peter Xu peterx@redhat.com Cc: Dev Jain dev.jain@arm.com Signed-off-by: David Hildenbrand david@redhat.com
Nice, big improvement!
Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com
Hopefully I didn't miss any review feedback.
All good afaict! :) the only thing would be to make the siglongjmp() conditional but it's not a big deal.
v1 -> v2:
- Rewrite using kselftest_harness, which simplifies a lot of things
- Add to .gitignore and run_vmtests.sh
- Register signal handler on demand
- Use volatile trick to force a read (not factoring out FORCE_READ just yet)
- Drop mprotect() test case
- Add some more comments why we test certain things
- Use NULL for mmap() first parameter instead of 0
- Smaller fixes
tools/testing/selftests/mm/.gitignore | 1 + tools/testing/selftests/mm/Makefile | 1 + tools/testing/selftests/mm/pfnmap.c | 196 ++++++++++++++++++++++ tools/testing/selftests/mm/run_vmtests.sh | 4 + 4 files changed, 202 insertions(+) create mode 100644 tools/testing/selftests/mm/pfnmap.c
diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore index 91db34941a143..824266982aa36 100644 --- a/tools/testing/selftests/mm/.gitignore +++ b/tools/testing/selftests/mm/.gitignore @@ -20,6 +20,7 @@ mremap_test on-fault-limit transhuge-stress pagemap_ioctl +pfnmap *.tmp* protection_keys protection_keys_32 diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile index ad4d6043a60f0..ae6f994d3add7 100644 --- a/tools/testing/selftests/mm/Makefile +++ b/tools/testing/selftests/mm/Makefile @@ -84,6 +84,7 @@ TEST_GEN_FILES += mremap_test TEST_GEN_FILES += mseal_test TEST_GEN_FILES += on-fault-limit TEST_GEN_FILES += pagemap_ioctl +TEST_GEN_FILES += pfnmap TEST_GEN_FILES += thuge-gen TEST_GEN_FILES += transhuge-stress TEST_GEN_FILES += uffd-stress diff --git a/tools/testing/selftests/mm/pfnmap.c b/tools/testing/selftests/mm/pfnmap.c new file mode 100644 index 0000000000000..8a9d19b6020c7 --- /dev/null +++ b/tools/testing/selftests/mm/pfnmap.c @@ -0,0 +1,196 @@ +// SPDX-License-Identifier: GPL-2.0-only +/*
- Basic VM_PFNMAP tests relying on mmap() of '/dev/mem'
- Copyright 2025, Red Hat, Inc.
- Author(s): David Hildenbrand david@redhat.com
- */
+#define _GNU_SOURCE +#include <stdlib.h> +#include <string.h> +#include <stdint.h> +#include <unistd.h> +#include <errno.h> +#include <fcntl.h> +#include <signal.h> +#include <setjmp.h> +#include <linux/mman.h> +#include <sys/mman.h> +#include <sys/wait.h>
+#include "../kselftest_harness.h" +#include "vm_util.h"
+static sigjmp_buf sigjmp_buf_env;
+static void signal_handler(int sig) +{
- siglongjmp(sigjmp_buf_env, -EFAULT);
+}
+static int test_read_access(char *addr, size_t size, size_t pagesize) +{
- size_t offs;
- int ret;
- if (signal(SIGSEGV, signal_handler) == SIG_ERR)
return -EINVAL;- ret = sigsetjmp(sigjmp_buf_env, 1);
- if (!ret) {
for (offs = 0; offs < size; offs += pagesize)/* Force a read that the compiler cannot optimize out. */*((volatile char *)(addr + offs));- }
- if (signal(SIGSEGV, signal_handler) == SIG_ERR)
return -EINVAL;- return ret;
+}
+FIXTURE(pfnmap) +{
- size_t pagesize;
- int dev_mem_fd;
- char *addr1;
- size_t size1;
- char *addr2;
- size_t size2;
+};
+FIXTURE_SETUP(pfnmap) +{
- self->pagesize = getpagesize();
- self->dev_mem_fd = open("/dev/mem", O_RDONLY);
- if (self->dev_mem_fd < 0)
SKIP(return, "Cannot open '/dev/mem'\n");- /* We'll require the first two pages throughout our tests ... */
- self->size1 = self->pagesize * 2;
- self->addr1 = mmap(NULL, self->size1, PROT_READ, MAP_SHARED,
self->dev_mem_fd, 0);- if (self->addr1 == MAP_FAILED)
SKIP(return, "Cannot mmap '/dev/mem'\n");- /* ... and want to be able to read from them. */
- if (test_read_access(self->addr1, self->size1, self->pagesize))
SKIP(return, "Cannot read-access mmap'ed '/dev/mem'\n");- self->size2 = 0;
- self->addr2 = MAP_FAILED;
+}
+FIXTURE_TEARDOWN(pfnmap) +{
- if (self->addr2 != MAP_FAILED)
munmap(self->addr2, self->size2);- if (self->addr1 != MAP_FAILED)
munmap(self->addr1, self->size1);- if (self->dev_mem_fd >= 0)
close(self->dev_mem_fd);+}
+TEST_F(pfnmap, madvise_disallowed) +{
- int advices[] = {
MADV_DONTNEED,MADV_DONTNEED_LOCKED,MADV_FREE,MADV_WIPEONFORK,MADV_COLD,MADV_PAGEOUT,MADV_POPULATE_READ,MADV_POPULATE_WRITE,- };
- int i;
- /* All these advices must be rejected. */
- for (i = 0; i < ARRAY_SIZE(advices); i++) {
EXPECT_LT(madvise(self->addr1, self->pagesize, advices[i]), 0);EXPECT_EQ(errno, EINVAL);- }
+}
+TEST_F(pfnmap, munmap_split) +{
- /*
* Unmap the first page. This munmap() call is not really expected to* fail, but we might be able to trigger other internal issues.*/- ASSERT_EQ(munmap(self->addr1, self->pagesize), 0);
- /*
* Remap the first page while the second page is still mapped. This* makes sure that any PAT tracking on x86 will allow for mmap()'ing* a page again while some parts of the first mmap() are still* around.*/- self->size2 = self->pagesize;
- self->addr2 = mmap(NULL, self->pagesize, PROT_READ, MAP_SHARED,
self->dev_mem_fd, 0);- ASSERT_NE(self->addr2, MAP_FAILED);
+}
+TEST_F(pfnmap, mremap_fixed) +{
- char *ret;
- /* Reserve a destination area. */
- self->size2 = self->size1;
- self->addr2 = mmap(NULL, self->size2, PROT_READ, MAP_ANON | MAP_PRIVATE,
-1, 0);- ASSERT_NE(self->addr2, MAP_FAILED);
- /* mremap() over our destination. */
- ret = mremap(self->addr1, self->size1, self->size2,
MREMAP_FIXED | MREMAP_MAYMOVE, self->addr2);- ASSERT_NE(ret, MAP_FAILED);
+}
+TEST_F(pfnmap, mremap_shrink) +{
- char *ret;
- /* Shrinking is expected to work. */
- ret = mremap(self->addr1, self->size1, self->size1 - self->pagesize, 0);
- ASSERT_NE(ret, MAP_FAILED);
+}
+TEST_F(pfnmap, mremap_expand) +{
- /*
* Growing is not expected to work, and getting it right would* be challenging. So this test primarily serves as an early warning* that something that probably should never work suddenly works.*/- self->size2 = self->size1 + self->pagesize;
- self->addr2 = mremap(self->addr1, self->size1, self->size2, MREMAP_MAYMOVE);
- ASSERT_EQ(self->addr2, MAP_FAILED);
+}
+TEST_F(pfnmap, fork) +{
- pid_t pid;
- int ret;
- /* fork() a child and test if the child can access the pages. */
- pid = fork();
- ASSERT_GE(pid, 0);
- if (!pid) {
EXPECT_EQ(test_read_access(self->addr1, self->size1,self->pagesize), 0);exit(0);- }
- wait(&ret);
- if (WIFEXITED(ret))
ret = WEXITSTATUS(ret);- else
ret = -EINVAL;- ASSERT_EQ(ret, 0);
+}
+TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh index 188b125bf1f6b..dddd1dd8af145 100755 --- a/tools/testing/selftests/mm/run_vmtests.sh +++ b/tools/testing/selftests/mm/run_vmtests.sh @@ -63,6 +63,8 @@ separated by spaces: test soft dirty page bit semantics
- pagemap test pagemap_scan IOCTL
+- pfnmap
- tests for VM_PFNMAP handling
- cow test copy-on-write semantics
- thp
@@ -472,6 +474,8 @@ fi CATEGORY="pagemap" run_test ./pagemap_ioctl +CATEGORY="pfnmap" run_test ./pfnmap
# COW tests CATEGORY="cow" run_test ./cow -- 2.49.0
linux-kselftest-mirror@lists.linaro.org
-
David Hildenbrand -
Lorenzo Stoakes