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bits are superseded by commit 26bab757d4 ("linux-user: Introduce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>
This commit is contained in:
Ilya Leoshkevich 2022-06-21 16:42:05 +02:00 committed by Laurent Vivier
parent 9263ba8473
commit 892a4f6a75
4 changed files with 68 additions and 6 deletions

View file

@ -65,6 +65,7 @@ abi_long do_syscall(CPUArchState *cpu_env, int num, abi_long arg1,
abi_long arg8);
extern __thread CPUState *thread_cpu;
G_NORETURN void cpu_loop(CPUArchState *env);
abi_long get_errno(abi_long ret);
const char *target_strerror(int err);
int get_osversion(void);
void init_qemu_uname_release(void);