Le 16/05/2018 à 16:47, Steve Mcpolin a écrit :
> When a guest mmap()'d a file, a transient MAP_ANONYMOUS mapping was
> created, which required the kernel to reserve this memory, then
> subsequently released by applying a mapping with just the requested
> flags and fd.
> This transient mapping causes spurious failures when the available
> memory is smaller than the mapping. This patch avoids this transient
> mapping.
>
> Signed-off-by: Steve Mcpolin <smcpo...@vmware.com>
> ---
> linux-user/mmap.c | 31 +++++++++++++++++++------------
> 1 file changed, 19 insertions(+), 12 deletions(-)
>
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index 9168a20..f91841f 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -453,21 +453,28 @@ abi_long target_mmap(abi_ulong start, abi_ulong len,
> int prot,
> /* Note: we prefer to control the mapping address. It is
> especially important if qemu_host_page_size >
> qemu_real_host_page_size */
> - p = mmap(g2h(start), host_len, prot,
> - flags | MAP_FIXED | MAP_ANONYMOUS, -1, 0);
> - if (p == MAP_FAILED)
> - goto fail;
> - /* update start so that it points to the file position at 'offset' */
> - host_start = (unsigned long)p;
> - if (!(flags & MAP_ANONYMOUS)) {
> - p = mmap(g2h(start), len, prot,
> + if (flags & MAP_ANONYMOUS) {
> + offset = 0;
> + host_offset = 0;
> + fd = -1;
> + }
> + p = mmap(g2h(start), len, prot,
> flags | MAP_FIXED, fd, host_offset);
> - if (p == MAP_FAILED) {
> - munmap(g2h(start), host_len);
> - goto fail;
> + host_start = (uintptr_t)p;
> + if (p != MAP_FAILED && host_len > HOST_PAGE_ALIGN(len)) {
> + void *q;
> + q = mmap(g2h(start + len), host_len - HOST_PAGE_ALIGN(len),
I think you should use REAL_HOST_PAGE_ALIGN(len) above.
This is the page size used by the host mmap() (it comes from
getpagesize()), whereas HOST_PAGE_ALIGN() can come from the command line
arguments.
Thanks,
Laurent
