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. Drop the explicit PAGE_ANON check, since anonymous mappings are
expected to have PAGE_PASSTHROUGH anyway.
Add PAGE_PASSTHROUGH to PAGE_STICKY in order to keep it on mprotect().
Signed-off-by: Ilya Leoshkevich <i...@linux.ibm.com>
Message-Id: <20220725125043.43048-1-...@linux.ibm.com>
---
accel/tcg/translate-all.c | 2 +-
include/exec/cpu-all.h | 6 ++++++
linux-user/mmap.c | 27 ++++++++++++++++++++++-----
3 files changed, 29 insertions(+), 6 deletions(-)
diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index b83161a081..a47cf38e38 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -2263,7 +2263,7 @@ int page_get_flags(target_ulong address)
#ifndef PAGE_TARGET_STICKY
#define PAGE_TARGET_STICKY 0
#endif
-#define PAGE_STICKY (PAGE_ANON | PAGE_TARGET_STICKY)
+#define PAGE_STICKY (PAGE_ANON | PAGE_PASSTHROUGH | PAGE_TARGET_STICKY)
/* Modify the flags of a page and invalidate the code if necessary.
The flag PAGE_WRITE_ORG is positioned automatically depending
diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index 491629b9ba..16b7df41bf 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 0x0800
+
#if defined(CONFIG_USER_ONLY)
void page_dump(FILE *f);
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index a5f1ab129c..3a0f67619a 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -425,7 +425,8 @@ 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();
@@ -538,6 +539,8 @@ 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;
@@ -620,6 +623,8 @@ 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:
@@ -627,7 +632,18 @@ 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)) {
@@ -846,7 +862,7 @@ 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_PASSTHROUGH)) {
return false;
}
}
@@ -888,8 +904,9 @@ abi_long target_madvise(abi_ulong start, abi_ulong len_in,
int advice)
* This is a hint, so ignoring and returning success is ok.
*
* 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.
+ * 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.
*/
mmap_lock();
if (advice == TARGET_MADV_DONTNEED &&
--
2.37.2
