[Qemu-devel] [PULL 7/9] KVM: Retry KVM_CREATE_VM on EINTR

[Paolo Bonzini]

From: thomas knych <address@hidden>

Upstreaming this change from Android 
(https://android-review.googlesource.com/54211).

On heavily loaded machines with many VM instances we see KVM_CREATE_VM
failing with EINTR on this path:

kvm_dev_ioctl_create_vm -> kvm_create_vm -> kvm_init_mmu_notifier -> 
mmu_notifier_register ->  do_mmu_notifier_register -> mm_take_all_locks

which checks if any signals have been raised while it was attaining locks
and returns EINTR.  Retrying the system call greatly improves reliability.

Cc: address@hidden
Signed-off-by: thomas knych <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
 kvm-all.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/kvm-all.c b/kvm-all.c
index 3937754..6df2ee1 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1442,16 +1442,22 @@ int kvm_init(void)
         nc++;
     }
 
-    s->vmfd = kvm_ioctl(s, KVM_CREATE_VM, 0);
-    if (s->vmfd < 0) {
+    do {
+        ret = kvm_ioctl(s, KVM_CREATE_VM, 0);
+    } while (ret == -EINTR);
+
+    if (ret < 0) {
+        fprintf(stderr, "ioctl(KVM_CREATE_VM) failed: %d %s\n", -s->vmfd,
+                strerror(-ret));
+
 #ifdef TARGET_S390X
         fprintf(stderr, "Please add the 'switch_amode' kernel parameter to "
                         "your host kernel command line\n");
 #endif
-        ret = s->vmfd;
         goto err;
     }
 
+    s->vmfd = ret;
     missing_cap = kvm_check_extension_list(s, kvm_required_capabilites);
     if (!missing_cap) {
         missing_cap =
-- 
1.8.3.1