Le 27/08/2018 à 10:40, Simon Hausmann a écrit :
> Most flags to madvise() are just hints, so typically ignoring the
> syscall and returning okay is fine. However applications exist that do
> rely on MADV_DONTNEED behavior to guarantee that upon subsequent access
> the mapping is refreshed from the backing file or zero for anonymous
> mappings. The file backed mappings this is tricky - hence the original
> comment - but for anonymous mappings it is safe to forward. We just need
> to remember which those mappings are, which is now stored in the flags.
>
> Cc: Riku Voipio <riku.voi...@iki.fi>
> Cc: Laurent Vivier <laur...@vivier.eu>
> Cc: Sami Nurmenniemi <sami.nurmenni...@qt.io>
> Signed-off-by: Simon Hausmann <simon.hausm...@qt.io>
>
> --
> v2:
> - align start and len on host page size
> v3:
> - align start and len to target page size as it may be bigger than
> host
> - use immediate return in do_syscall
> - forward MADV_DONTNEED advice only for anonymously mapped pages
> - remember which mappings are anonymous in the page flags and preserve
> those bits across mprotect calls.
> ---
> accel/tcg/translate-all.c | 8 +++++--
> bsd-user/mmap.c | 8 +++----
> include/exec/cpu-all.h | 11 ++++++++-
> linux-user/elfload.c | 3 ++-
> linux-user/mmap.c | 49 +++++++++++++++++++++++++++++++++++----
> linux-user/qemu.h | 1 +
> linux-user/syscall.c | 12 ++++------
> 7 files changed, 72 insertions(+), 20 deletions(-)
>
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 898c3bb3d1..467fbd9aeb 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -2481,7 +2481,8 @@ int page_get_flags(target_ulong address)
> /* Modify the flags of a page and invalidate the code if necessary.
> The flag PAGE_WRITE_ORG is positioned automatically depending
> on PAGE_WRITE. The mmap_lock should already be held. */
> -void page_set_flags(target_ulong start, target_ulong end, int flags)
> +void page_set_flags(target_ulong start, target_ulong end, int flags,
> + enum page_set_flags_mode mode)
Is it possible to not add the mode, and only use "flags" to set the new
flag? Using page_get_flags() to keep flags that needed to be kept?
> {
> target_ulong addr, len;
>
> @@ -2513,7 +2514,10 @@ void page_set_flags(target_ulong start, target_ulong
> end, int flags)
> p->first_tb) {
> tb_invalidate_phys_page(addr, 0);
> }
> - p->flags = flags;
> + if (mode == PAGE_SET_ALL_FLAGS)
> + p->flags = flags;
> + else /* PAGE_SET_PROTECTION */
> + p->flags |= (p->flags & ~(PAGE_BITS - 1)) | (flags & PAGE_BITS);
> }
> }
>
> diff --git a/bsd-user/mmap.c b/bsd-user/mmap.c
> index 17f4cd80aa..4bfac81af4 100644
> --- a/bsd-user/mmap.c
> +++ b/bsd-user/mmap.c
> @@ -125,7 +125,7 @@ int target_mprotect(abi_ulong start, abi_ulong len, int
> prot)
> if (ret != 0)
> goto error;
> }
> - page_set_flags(start, start + len, prot | PAGE_VALID);
> + page_set_flags(start, start + len, prot, PAGE_SET_PROTECTION);
Why do you remove the PAGE_VALID flag?
...
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index 8638612aec..c59cf4359c 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -1702,7 +1702,8 @@ static void zero_bss(abi_ulong elf_bss, abi_ulong
> last_bss, int prot)
>
> /* Ensure that the bss page(s) are valid */
> if ((page_get_flags(last_bss-1) & prot) != prot) {
> - page_set_flags(elf_bss & TARGET_PAGE_MASK, last_bss, prot |
> PAGE_VALID);
> + page_set_flags(elf_bss & TARGET_PAGE_MASK, last_bss, prot,
> + PAGE_SET_PROTECTION);
> }
PAGE_VALID?
>
> if (host_start < host_map_start) {
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index 41e0983ce8..fff29ee04b 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -124,7 +124,7 @@ int target_mprotect(abi_ulong start, abi_ulong len, int
> prot)
> if (ret != 0)
> goto error;
> }
> - page_set_flags(start, start + len, prot | PAGE_VALID);
> + page_set_flags(start, start + len, prot, PAGE_SET_PROTECTION);
> mmap_unlock();
PAGE_VALID?
...
> +int target_madvise(abi_ulong start, abi_ulong len, int advice)
> +{
> + abi_ulong end, addr;
> + int ret;
> +
> + len = TARGET_PAGE_ALIGN(len);
> + start &= TARGET_PAGE_MASK;
> +
> + if (!guest_range_valid(start, len)) {
> + errno = EINVAL;
> + return -1;
> + }
> +
> + /* A straight passthrough may not be safe because qemu sometimes
> + turns private file-backed mappings into anonymous mappings.
> + Most flags are hints so we ignore them.
> + One exception is made for MADV_DONTNEED on anonymous mappings,
> + that applications may rely on to zero out pages. */
> + if (advice & MADV_DONTNEED) {
> + end = start + len;
> + for (addr = start; addr < end; addr += TARGET_PAGE_SIZE) {
> + if (page_get_flags(addr) & PAGE_MAP_ANONYMOUS) {
> + ret = madvise(g2h(addr), TARGET_PAGE_SIZE, MADV_DONTNEED);
these values must be aligned on host page size.
Thanks,
Laurent
