Re: [Qemu-devel] [PATCH qemu] kvm-irqchip: Only do explicit IRQ routing commit when IRQCHIP is in use

[Peter Xu]

On Wed, Jul 27, 2016 at 05:51:46PM +1000, Alexey Kardashevskiy wrote:
> 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
> kvm_irqchip_commit_routes.
> 
> 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 
> /home/aik/p/qemu-ddw/kvm-all.c:1050
> 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 
> /home/aik/p/qemu-ddw/kvm-all.c:1050
> #1  0x000000001010fcd4 in vfio_update_kvm_msi_virq (vector=0x3fffa8006a10, 
> msg=..., pdev=0x1101f300) at /h
> ome/aik/p/qemu-ddw/hw/vfio/pci.c:461
> #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/
> hw/vfio/pci.c:557
> #4  0x00000000103f64c4 in msix_fire_vector_notifier (dev=0x1101f300, 
> vector=0x0, is_masked=0x0) at /home/a
> ik/p/qemu-ddw/hw/pci/msix.c:111
> #5  0x00000000103f6594 in msix_handle_mask_update (dev=0x1101f300, 
> vector=0x0, was_masked=0x1) at /home/ai
> k/p/qemu-ddw/hw/pci/msix.c:124
> #6  0x00000000103f6928 in msix_table_mmio_write (opaque=0x1101f300, addr=0xc, 
> val=0x0, size=0x4) at /home/
> aik/p/qemu-ddw/hw/pci/msix.c:186
> #7  0x0000000010099738 in memory_region_write_accessor (mr=0x1101f838, 
> addr=0xc, value=0x3fffb663df50, siz
> e=0x4, shift=0x0, mask=0xffffffff, attrs=...) at 
> /home/aik/p/qemu-ddw/memory.c:525
> #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
> w/exec.c:2580
> #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 
> /home/aik/p/qemu-ddw/exec.c:2739
> #13 0x0000000010094cb8 in kvm_cpu_exec (cpu=0x3fffb6e76db0) at 
> /home/aik/p/qemu-ddw/kvm-all.c:1952
> #14 0x0000000010072764 in qemu_kvm_cpu_thread_fn (arg=0x3fffb6e76db0) at 
> /home/aik/p/qemu-ddw/cpus.c:1078
> #15 0x00003fffb7a184a0 in start_thread (arg=0x3fffb663ec90) at 
> pthread_create.c:335
> #16 0x00003fffb7957e74 in clone () at 
> ../sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S:96
> (gdb)
> ---
>  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);

Sorry for the trouble. How about this one:

diff --git a/kvm-all.c b/kvm-all.c
index ef81ca5..4b3e330 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1047,6 +1047,10 @@ void kvm_irqchip_commit_routes(KVMState *s)
 {
     int ret;

+    if (kvm_gsi_direct_mapping()) {
+        return 0;
+    }
+
     s->irq_routes->flags = 0;
     trace_kvm_irqchip_commit_routes();
     ret = kvm_vm_ioctl(s, KVM_SET_GSI_ROUTING, s->irq_routes);

I don't know whether irq_routes will be NULL for all GSI direct
mapping case... at least this can have kvm_irqchip_*() APIs got
aligned.

Thanks,

-- peterx