On 24/12/22 16:18, Richard Henderson wrote:
As in page_get_flags, we need to try again with the mmap
lock held if we fail a page lookup.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
accel/tcg/user-exec.c | 39 ++++++++++++++++++++++++++++++++-------
1 file changed, 32 insertions(+), 7 deletions(-)
diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c
index 2c5c10d2e6..c72a806203 100644
--- a/accel/tcg/user-exec.c
+++ b/accel/tcg/user-exec.c
@@ -525,6 +525,7 @@ void page_set_flags(target_ulong start, target_ulong end,
int flags)
int page_check_range(target_ulong start, target_ulong len, int flags)
{
target_ulong last;
+ int locked, ret;
have_mmap_lock() returns a boolean, can we declare 'locked'
as such, ...
if (len == 0) {
return 0; /* trivial length */
@@ -535,42 +536,66 @@ int page_check_range(target_ulong start, target_ulong
len, int flags)
return -1; /* wrap around */
}
+ locked = have_mmap_lock();
while (true) {
PageFlagsNode *p = pageflags_find(start, last);
int missing;
if (!p) {
- return -1; /* entire region invalid */
+ if (!locked) {
+ /*
+ * Lockless lookups have false negatives.
+ * Retry with the lock held.
+ */
+ mmap_lock();
+ locked = -1;
... skip this confusing assignation, ...
+ p = pageflags_find(start, last);
+ }
+ if (!p) {
+ ret = -1; /* entire region invalid */
+ break;
+ }
}
if (start < p->itree.start) {
- return -1; /* initial bytes invalid */
+ ret = -1; /* initial bytes invalid */
+ break;
}
missing = flags & ~p->flags;
if (missing & PAGE_READ) {
- return -1; /* page not readable */
+ ret = -1; /* page not readable */
+ break;
}
if (missing & PAGE_WRITE) {
if (!(p->flags & PAGE_WRITE_ORG)) {
- return -1; /* page not writable */
+ ret = -1; /* page not writable */
+ break;
}
/* Asking about writable, but has been protected: undo. */
if (!page_unprotect(start, 0)) {
- return -1;
+ ret = -1;
+ break;
}
/* TODO: page_unprotect should take a range, not a single page. */
if (last - start < TARGET_PAGE_SIZE) {
- return 0; /* ok */
+ ret = 0; /* ok */
+ break;
}
start += TARGET_PAGE_SIZE;
continue;
}
if (last <= p->itree.last) {
- return 0; /* ok */
+ ret = 0; /* ok */
+ break;
}
start = p->itree.last + 1;
}
+
+ if (locked < 0) {
... and check for !locked here?