kvm: Fix kvm_vm_ioctl() and kvm_device_ioctl() return value

These functions wrap ioctl().  When ioctl() fails, it sets @errno.
The wrappers then return that @errno negated.

Except they call accel_ioctl_end() between calling ioctl() and reading
@errno.  accel_ioctl_end() can clobber @errno, e.g. when a futex()
system call fails.  Seems unlikely, but it's a bug all the same.

Fix by retrieving @errno before calling accel_ioctl_end().

Fixes: a27dd2de68f3 (KVM: keep track of running ioctls)
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20251128152050.3417834-1-armbru@redhat.com>

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index f9254ae6546671e4569c190a098447becbdac0e0..28006d73c51e1ed6cb707f9c225291a48f8a2e11 100644 (file)
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -3373,10 +3373,10 @@ int kvm_vm_ioctl(KVMState *s, unsigned long type, ...)
     trace_kvm_vm_ioctl(type, arg);
     accel_ioctl_begin();
     ret = ioctl(s->vmfd, type, arg);
-    accel_ioctl_end();
     if (ret == -1) {
         ret = -errno;
     }
+    accel_ioctl_end();
     return ret;
 }
 
@@ -3413,10 +3413,10 @@ int kvm_device_ioctl(int fd, unsigned long type, ...)
     trace_kvm_device_ioctl(fd, type, arg);
     accel_ioctl_begin();
     ret = ioctl(fd, type, arg);
-    accel_ioctl_end();
     if (ret == -1) {
         ret = -errno;
     }
+    accel_ioctl_end();
     return ret;
 }