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[Qemu-devel] [PATCH qemu] kvm-irqchip: Only do explicit IRQ routing comm

From: Alexey Kardashevskiy
Subject: [Qemu-devel] [PATCH qemu] kvm-irqchip: Only do explicit IRQ routing commit when IRQCHIP is in use
Date: Wed, 27 Jul 2016 17:51:46 +1000

3f1fea0fb5bf "kvm-irqchip: do explicit commit when update irq" produces
a crash on pseries guest running with VFIO on POWER8 machine as
it does not support KVM_CAP_IRQCHIP (KVM_CAP_IRQ_XICS is there instead).
At the result, KVMState::irq_routes is NULL when VFIO calls

This makes the routing update conditional.

Signed-off-by: Alexey Kardashevskiy <address@hidden>

Or I am too late and there is the fix? Could not find any.

This is the backtrace:

Thread 4 "qemu-system-ppc" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x3fffb663ec90 (LWP 11852)]
0x0000000010091fa4 in kvm_irqchip_commit_routes (s=0x10eff3b0) at 
1050        s->irq_routes->flags = 0;
(gdb) p s
$2 = (KVMState *) 0x10eff3b0
(gdb) p s->irq_routes
$3 = (struct kvm_irq_routing *) 0x0
(gdb) bt
#0  0x0000000010091fa4 in kvm_irqchip_commit_routes (s=0x10eff3b0) at 
#1  0x000000001010fcd4 in vfio_update_kvm_msi_virq (vector=0x3fffa8006a10, 
msg=..., pdev=0x1101f300) at /h
#2  0x000000001010fe58 in vfio_msix_vector_do_use (pdev=0x1101f300, nr=0x0, 
msg=0x3fffb663dd00, handler=0x
1010f5e8 <vfio_msi_interrupt>) at /home/aik/p/qemu-ddw/hw/vfio/pci.c:496
#3  0x000000001011010c in vfio_msix_vector_use (pdev=0x1101f300, nr=0x0, 
msg=...) at /home/aik/p/qemu-ddw/
#4  0x00000000103f64c4 in msix_fire_vector_notifier (dev=0x1101f300, 
vector=0x0, is_masked=0x0) at /home/a
#5  0x00000000103f6594 in msix_handle_mask_update (dev=0x1101f300, vector=0x0, 
was_masked=0x1) at /home/ai
#6  0x00000000103f6928 in msix_table_mmio_write (opaque=0x1101f300, addr=0xc, 
val=0x0, size=0x4) at /home/
#7  0x0000000010099738 in memory_region_write_accessor (mr=0x1101f838, 
addr=0xc, value=0x3fffb663df50, siz
e=0x4, shift=0x0, mask=0xffffffff, attrs=...) at 
#8  0x0000000010099a94 in access_with_adjusted_size (addr=0xc, 
value=0x3fffb663df50, size=0x4, access_size
_min=0x1, access_size_max=0x4, access=0x100995f8 
<memory_region_write_accessor>, mr=0x1101f838, attrs=...)
 at /home/aik/p/qemu-ddw/memory.c:591
#9  0x000000001009cb0c in memory_region_dispatch_write (mr=0x1101f838, 
addr=0xc, data=0x0, size=0x4, attrs
=...) at /home/aik/p/qemu-ddw/memory.c:1262
#10 0x0000000010015300 in address_space_write_continue (as=0x109b3958 
<address_space_memory>, addr=0x10120
00200c, attrs=..., buf=0x3fffb5e20028 "", len=0x4, addr1=0xc, l=0x4, 
mr=0x1101f838) at /home/aik/p/qemu-dd
#11 0x0000000010015558 in address_space_write (as=0x109b3958 
<address_space_memory>, addr=0x1012000200c, a
ttrs=..., buf=0x3fffb5e20028 "", len=0x4) at /home/aik/p/qemu-ddw/exec.c:2637
#12 0x00000000100159e4 in address_space_rw (as=0x109b3958 
<address_space_memory>, addr=0x1012000200c, attr
s=..., buf=0x3fffb5e20028 "", len=0x4, is_write=0x1) at 
#13 0x0000000010094cb8 in kvm_cpu_exec (cpu=0x3fffb6e76db0) at 
#14 0x0000000010072764 in qemu_kvm_cpu_thread_fn (arg=0x3fffb6e76db0) at 
#15 0x00003fffb7a184a0 in start_thread (arg=0x3fffb663ec90) at 
#16 0x00003fffb7957e74 in clone () at 
 kvm-all.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kvm-all.c b/kvm-all.c
index 3764ba9..028fdcb 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1047,6 +1047,10 @@ void kvm_irqchip_commit_routes(KVMState *s)
     int ret;
+    if (!s->irq_routes) {
+        return;
+    }
     s->irq_routes->flags = 0;
     ret = kvm_vm_ioctl(s, KVM_SET_GSI_ROUTING, s->irq_routes);
     assert(ret == 0);

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