[PATCH 0/2] linux-user: return ENOMEM from madvise on unmapped ranges

[PATCH 0/2] linux-user: return ENOMEM from madvise on unmapped ranges

[Roi Klevansky]

The kernel fails madvise() with ENOMEM when it is given a partially or a
fully unmapped address range. qemu-user differed from this and returned
0 instead.

Patch 1 makes target_madvise() check the range with page_check_range()
and potentially fail with ENOMEM while still giving precedence to
advice specific errors.

Patch 2 adds test cases, calling madvise() with partially and fully
unmapped address ranges.

Roi Klevansky (2):
  linux-user: return ENOMEM from madvise on unmapped ranges
  tests/tcg: add linux-user test for madvise returning ENOMEM

 linux-user/mmap.c                         |  7 +++-
 tests/tcg/multiarch/linux/linux-madvise.c | 43 +++++++++++++++++++++++
 2 files changed, 49 insertions(+), 1 deletion(-)

-- 
2.55.0

[PATCH 1/2] linux-user: return ENOMEM from madvise on unmapped ranges

[Roi Klevansky]

The kernel fails with ENOMEM when madvise() is called with a partially
or fully unmapped address range. This fix allows target_madvise() to
emulate this behavior by calling page_check_range() upfront while still
allowing advice specific errors to take precedence.

Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4382
Signed-off-by: Roi Klevansky <roiklevansky@gmail.com>
---
 linux-user/mmap.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index cc0c2ee6c2..e5195cf501 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -1305,8 +1305,14 @@ abi_long target_madvise(abi_ulong start, abi_ulong len_in, int advice)
      * success, which is broken but some userspace programs fail to work
      * otherwise. Completely implementing such emulation is quite complicated
      * though.
+     *
+     * When some (or all) of the pages in the range are not mapped, madvise
+     * should fail with -ENOMEM. If another error occurs, its value is
+     * returned instead.
      */
     mmap_lock();
+    ret = page_check_range(start, len, PAGE_VALID) ? 0 : -TARGET_ENOMEM;
+
     switch (advice) {
     case MADV_NORMAL:
     case MADV_RANDOM:
@@ -1316,7 +1322,6 @@ abi_long target_madvise(abi_ulong start, abi_ulong len_in, int advice)
     case MADV_FREE:
     case MADV_COLD:
     case MADV_PAGEOUT:
-        ret = 0; /* OK */
         break;
     case MADV_REMOVE:
         ret = -EOPNOTSUPP;
-- 
2.55.0

[PATCH 2/2] tests/tcg: add linux-user test for madvise returning ENOMEM

[Roi Klevansky]

Add tests for madvise() under linux-user with partially and fully
unmapped address ranges, making sure it returns ENOMEM, just like
the kernel does.

Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4382
Signed-off-by: Roi Klevansky <roiklevansky@gmail.com>
---
 tests/tcg/multiarch/linux/linux-madvise.c | 43 +++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/tests/tcg/multiarch/linux/linux-madvise.c b/tests/tcg/multiarch/linux/linux-madvise.c
index 539fb3b772..b7a52abb6c 100644
--- a/tests/tcg/multiarch/linux/linux-madvise.c
+++ b/tests/tcg/multiarch/linux/linux-madvise.c
@@ -1,4 +1,5 @@
 #include <assert.h>
+#include <errno.h>
 #include <stdlib.h>
 #include <sys/mman.h>
 #include <unistd.h>
@@ -63,10 +64,52 @@ static void test_file(void)
     assert(ret == 0);
 }
 
+static void test_mapped_and_unmapped(void)
+{
+    int pagesize = getpagesize();
+    void *page;
+    int ret;
+
+    page = mmap(NULL, pagesize, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+    assert(page != MAP_FAILED);
+
+    ret = madvise(page, pagesize, MADV_NORMAL);
+    assert(ret == 0);
+
+    ret = munmap(page, pagesize);
+    assert(ret == 0);
+
+    ret = madvise(page, pagesize, MADV_NORMAL);
+    assert(ret == -1);
+    assert(errno == ENOMEM);
+}
+
+static void test_partially_unmapped_enomem(void)
+{
+    int pagesize = getpagesize();
+    void *page;
+    int ret;
+
+    page = mmap(NULL, 3 * pagesize, PROT_READ,
+                MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+    assert(page != MAP_FAILED);
+    ret = munmap((char *)page + pagesize, pagesize);
+    assert(ret == 0);
+
+    ret = madvise(page, 3 * pagesize, MADV_NORMAL);
+    assert(ret == -1);
+    assert(errno == ENOMEM);
+
+    ret = munmap(page, 3 * pagesize);
+    assert(ret == 0);
+}
+
 int main(void)
 {
     test_anonymous();
     test_file();
+    test_mapped_and_unmapped();
+    test_partially_unmapped_enomem();
 
     return EXIT_SUCCESS;
 }
-- 
2.55.0