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Re: [Qemu-devel] [PATCH v3] linux-user: Remove extra mapping
From: |
Laurent Vivier |
Subject: |
Re: [Qemu-devel] [PATCH v3] linux-user: Remove extra mapping |
Date: |
Tue, 29 May 2018 21:20:31 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 |
Le 29/05/2018 à 20:15, Steve Mcpolin a écrit :
> When a guest mmap()'d a file, an anonymous mapping was created to
> align different host and client page granularity and provide for
> beyond EOF mappings. The file was then mapped ontop of this mapping,
> releasing the memory reserved by it. A file based mmap does not reserve
> memory, but the anonymous map does; thus this anonymous mapping could
> could cause spurious failures.
>
> This patch minimizes the size of the anonymous mapping to prevent spurious
> failures.
>
> Signed-off-by: Steve Mcpolin <address@hidden>
> ---
v3:
add missing flags in the second mmap()
v2:
use REAL_HOST_PAGE_ALIGN(len) instead of HOST_PAGE_ALIGN(len)
> linux-user/mmap.c | 32 ++++++++++++++++++++------------
> 1 file changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index 9168a20..7a975c8 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -453,21 +453,29 @@ 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 > REAL_HOST_PAGE_ALIGN(len)) {
> + void *q;
> + q = mmap(g2h(start + len), host_len - REAL_HOST_PAGE_ALIGN(len),
> + prot, MAP_FIXED | (flags & MAP_TYPE) | MAP_ANONYMOUS,
Why do you restrict the flags with MAP_TYPE? Original code was not doing
that. Is this needed?
Thanks,
Laurent