On Fri, 2022-07-01 at 15:52 +0200, Ilya Leoshkevich wrote:
> This is a follow-up for commit 892a4f6a750a ("linux-user: Add partial
> support for MADV_DONTNEED"), which added passthrough for anonymous
> mappings. File mappings can be handled in a similar manner.
>
> In order to do that, mark pages, for which mmap() was passed through,
> with PAGE_PASSTHROUGH, and then allow madvise() passthrough for these
> pages as well.
>
> Signed-off-by: Ilya Leoshkevich <i...@linux.ibm.com>
> ---
> include/exec/cpu-all.h | 6 ++++++
> linux-user/mmap.c | 25 +++++++++++++++++++++----
> 2 files changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
> index f5bda2c3ca..fbdbc0fdec 100644
> --- a/include/exec/cpu-all.h
> +++ b/include/exec/cpu-all.h
> @@ -262,6 +262,12 @@ extern const TargetPageBits target_page;
> #define PAGE_TARGET_1 0x0200
> #define PAGE_TARGET_2 0x0400
>
> +/*
> + * For linux-user, indicates that the page is mapped with the same
> semantics
> + * in both guest and host.
> + */
> +#define PAGE_PASSTHROUGH 0x0080
> +
> #if defined(CONFIG_USER_ONLY)
> void page_dump(FILE *f);
>
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index 4e7a6be6ee..58622a0c15 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -424,7 +424,8 @@ abi_ulong mmap_find_vma(abi_ulong start,
> abi_ulong size, abi_ulong align)
> abi_long target_mmap(abi_ulong start, abi_ulong len, int
> target_prot,
> int flags, int fd, abi_ulong offset)
> {
> - abi_ulong ret, end, real_start, real_end, retaddr, host_offset,
> host_len;
> + abi_ulong ret, end, real_start, real_end, retaddr, host_offset,
> host_len,
> + passthrough_start = -1, passthrough_end = -1;
> int page_flags, host_prot;
>
> mmap_lock();
> @@ -537,6 +538,8 @@ abi_long target_mmap(abi_ulong start, abi_ulong
> len, int target_prot,
> host_start += offset - host_offset;
> }
> start = h2g(host_start);
> + passthrough_start = start;
> + passthrough_end = start + len;
> } else {
> if (start & ~TARGET_PAGE_MASK) {
> errno = EINVAL;
> @@ -619,6 +622,8 @@ abi_long target_mmap(abi_ulong start, abi_ulong
> len, int target_prot,
> host_prot, flags, fd, offset1);
> if (p == MAP_FAILED)
> goto fail;
> + passthrough_start = real_start;
> + passthrough_end = real_end;
> }
> }
> the_end1:
> @@ -626,7 +631,18 @@ abi_long target_mmap(abi_ulong start, abi_ulong
> len, int target_prot,
> page_flags |= PAGE_ANON;
> }
> page_flags |= PAGE_RESET;
> - page_set_flags(start, start + len, page_flags);
> + if (passthrough_start == passthrough_end) {
> + page_set_flags(start, start + len, page_flags);
> + } else {
> + if (start != passthrough_start) {
> + page_set_flags(start, passthrough_start, page_flags);
> + }
> + page_set_flags(passthrough_start, passthrough_end,
> + page_flags | PAGE_PASSTHROUGH);
> + if (passthrough_end != start + len) {
> + page_set_flags(passthrough_end, start + len,
> page_flags);
> + }
> + }
> the_end:
> trace_target_mmap_complete(start);
> if (qemu_loglevel_mask(CPU_LOG_PAGE)) {
> @@ -845,7 +861,7 @@ static bool
> can_passthrough_madv_dontneed(abi_ulong start, abi_ulong end)
> }
>
> for (addr = start; addr < end; addr += TARGET_PAGE_SIZE) {
> - if (!(page_get_flags(addr) & PAGE_ANON)) {
> + if (!(page_get_flags(addr) & (PAGE_ANON |
> PAGE_PASSTHROUGH))) {
> return false;
> }
> }
> @@ -888,7 +904,8 @@ abi_long target_madvise(abi_ulong start,
> abi_ulong len_in, int advice)
> *
> * This breaks MADV_DONTNEED, completely implementing which is
> quite
> * complicated. However, there is one low-hanging fruit: host-
> page-aligned
> - * anonymous mappings. In this case passthrough is safe, so do
> it.
> + * anonymous mappings or mappings that are known to have the
> same semantics
> + * in the host and the guest. In this case passthrough is safe,
> so do it.
> */
> mmap_lock();
> if ((advice & MADV_DONTNEED) &&
Ping:
https://patchew.org/QEMU/20220701135207.2710488-1-...@linux.ibm.com/
Also +Cc: Richard and Paolo.
