diff options
| author | Ilya Leoshkevich <iii@linux.ibm.com> | 2022-06-21 16:42:05 +0200 |
|---|---|---|
| committer | Laurent Vivier <laurent@vivier.eu> | 2022-06-24 10:00:00 +0200 |
| commit | 892a4f6a750abceeda4c1ee8324f58f82fd6bd89 (patch) | |
| tree | e0653c18cff17f077638a38762d310072d649c7e /linux-user/syscall.c | |
| parent | 9263ba847352c2ec2fc37ad7f7d0558332bd077f (diff) | |
linux-user: Add partial support for MADV_DONTNEED
Currently QEMU ignores madvise(MADV_DONTNEED), which break apps that
rely on this for zeroing out memory [1]. Improve the situation by doing
a passthrough when the range in question is a host-page-aligned
anonymous mapping.
This is based on the patches from Simon Hausmann [2] and Chris Fallin
[3]. The structure is taken from Simon's patch. The PAGE_MAP_ANONYMOUS
bits are superseded by commit 26bab757d41b ("linux-user: Introduce
PAGE_ANON"). In the end the patch acts like the one from Chris: we
either pass-through the entire syscall, or do nothing, since doing this
only partially would not help the affected applications much. Finally,
add some extra checks to match the behavior of the Linux kernel [4].
[1] https://gitlab.com/qemu-project/qemu/-/issues/326
[2] https://patchew.org/QEMU/20180827084037.25316-1-simon.hausmann@qt.io/
[3] https://github.com/bytecodealliance/wasmtime/blob/v0.37.0/ci/qemu-madvise.patch
[4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/madvise.c?h=v5.19-rc3#n1368
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220621144205.158452-1-iii@linux.ibm.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Diffstat (limited to 'linux-user/syscall.c')
| -rw-r--r-- | linux-user/syscall.c | 8 |
1 files changed, 2 insertions, 6 deletions
diff --git a/linux-user/syscall.c b/linux-user/syscall.c index f55cdebee5..8f68f255c0 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -538,7 +538,7 @@ static inline int target_to_host_errno(int target_errno) } } -static inline abi_long get_errno(abi_long ret) +abi_long get_errno(abi_long ret) { if (ret == -1) return -host_to_target_errno(errno); @@ -11807,11 +11807,7 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1, #ifdef TARGET_NR_madvise case TARGET_NR_madvise: - /* A straight passthrough may not be safe because qemu sometimes - turns private file-backed mappings into anonymous mappings. - This will break MADV_DONTNEED. - This is a hint, so ignoring and returning success is ok. */ - return 0; + return target_madvise(arg1, arg2, arg3); #endif #ifdef TARGET_NR_fcntl64 case TARGET_NR_fcntl64: |