linux-user: Set CF_PARALLEL when mapping shared memory
Signal the translator to use host atomic instructions for
guest operations, insofar as it is possible. This is the
best we can do to allow the guest to interact atomically
with other processes.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/121
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210612060828.695332-1-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 974dd46..54037db 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -4603,6 +4603,7 @@
static inline abi_ulong do_shmat(CPUArchState *cpu_env,
int shmid, abi_ulong shmaddr, int shmflg)
{
+ CPUState *cpu = env_cpu(cpu_env);
abi_long raddr;
void *host_raddr;
struct shmid_ds shm_info;
@@ -4633,6 +4634,17 @@
mmap_lock();
+ /*
+ * We're mapping shared memory, so ensure we generate code for parallel
+ * execution and flush old translations. This will work up to the level
+ * supported by the host -- anything that requires EXCP_ATOMIC will not
+ * be atomic with respect to an external process.
+ */
+ if (!(cpu->tcg_cflags & CF_PARALLEL)) {
+ cpu->tcg_cflags |= CF_PARALLEL;
+ tb_flush(cpu);
+ }
+
if (shmaddr)
host_raddr = shmat(shmid, (void *)g2h_untagged(shmaddr), shmflg);
else {
