diff options
| -rw-r--r-- | linux-user/mmap.c | 56 |
1 files changed, 43 insertions, 13 deletions
diff --git a/linux-user/mmap.c b/linux-user/mmap.c index 10f5079..28135c9 100644 --- a/linux-user/mmap.c +++ b/linux-user/mmap.c @@ -857,7 +857,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size, return new_addr; } -static bool can_passthrough_madv_dontneed(abi_ulong start, abi_ulong end) +static bool can_passthrough_madvise(abi_ulong start, abi_ulong end) { ulong addr; @@ -901,23 +901,53 @@ abi_long target_madvise(abi_ulong start, abi_ulong len_in, int advice) return -TARGET_EINVAL; } + /* Translate for some architectures which have different MADV_xxx values */ + switch (advice) { + case TARGET_MADV_DONTNEED: /* alpha */ + advice = MADV_DONTNEED; + break; + case TARGET_MADV_WIPEONFORK: /* parisc */ + advice = MADV_WIPEONFORK; + break; + case TARGET_MADV_KEEPONFORK: /* parisc */ + advice = MADV_KEEPONFORK; + break; + /* we do not care about the other MADV_xxx values yet */ + } + /* - * A straight passthrough may not be safe because qemu sometimes turns - * private file-backed mappings into anonymous mappings. + * Most advice values are hints, so ignoring and returning success is ok. + * + * However, some advice values such as MADV_DONTNEED, MADV_WIPEONFORK and + * MADV_KEEPONFORK are not hints and need to be emulated. * - * This is a hint, so ignoring and returning success is ok. + * A straight passthrough for those may not be safe because qemu sometimes + * turns private file-backed mappings into anonymous mappings. + * can_passthrough_madvise() helps to check if a passthrough is possible by + * comparing mappings that are known to have the same semantics in the host + * and the guest. In this case passthrough is safe. * - * This breaks MADV_DONTNEED, completely implementing which is quite - * complicated. However, there is one low-hanging fruit: mappings that are - * known to have the same semantics in the host and the guest. In this case - * passthrough is safe, so do it. + * We pass through MADV_WIPEONFORK and MADV_KEEPONFORK if possible and + * return failure if not. + * + * MADV_DONTNEED is passed through as well, if possible. + * If passthrough isn't possible, we nevertheless (wrongly!) return + * success, which is broken but some userspace programs fail to work + * otherwise. Completely implementing such emulation is quite complicated + * though. */ mmap_lock(); - if (advice == TARGET_MADV_DONTNEED && - can_passthrough_madv_dontneed(start, end)) { - ret = get_errno(madvise(g2h_untagged(start), len, MADV_DONTNEED)); - if (ret == 0) { - page_reset_target_data(start, start + len); + switch (advice) { + case MADV_WIPEONFORK: + case MADV_KEEPONFORK: + ret = -EINVAL; + /* fall through */ + case MADV_DONTNEED: + if (can_passthrough_madvise(start, end)) { + ret = get_errno(madvise(g2h_untagged(start), len, advice)); + if ((advice == MADV_DONTNEED) && (ret == 0)) { + page_reset_target_data(start, start + len); + } } } mmap_unlock(); |