passthroughed msix device

[DuanZhenzhong <zhenzhong.duan@oracle.com>]

Hi maintainer,

Reprodue an bug on xen-unstable, it's an irq affinity issue for 
passthroughed msix device to uek1 pvhvm(2.6.32 stable).
I passthrough two mptsas devices(0000:0d:0.0, 0000:1f:0.0) to a pvhvm, 
irq affinity can't be changed.
Step to reproduce is as below:
1. xl -f pci-assignable-add 0000:0d:0.0; xl -f pci-assignable-add 
0000:1f:0.0
2.xm cr -c vm.cfg
[root@rac10box2 ~]# cat /proc/interrupts |grep mpt2sas0
 48:     340449          0          0          0          0 0          
0          0          0          0          0 0   PCI-MSI-edge      
mpt2sas0-msix0
[root@rac10box2 ~]# cat /proc/irq/48/smp_affinity
0fff
[root@rac10box2 ~]# echo 2>/proc/irq/48/smp_affinity
[root@rac10box2 ~]# cat /proc/irq/48/smp_affinity
0002
[root@rac10box2 ~]# cat /proc/interrupts |grep mpt
 48:     342051        0          0          0          0 0          
0          0          0          0          0 0   PCI-MSI-edge      
mpt2sas0-msix0
After change affinity to vcpu1, interrupt still happen on vcpu0. And 
sometimes we got "/No irq handler for vector (irq -1)/" and panic.
qemu-dm.log shows error:
pt_msixctrl_reg_write: guest enabling MSI-X, disable MSI-INTx translation
pci_intx: intx=1
pt_msi_disable: Unmap msi with pirq 4f
pt_msix_update_one: Update msix entry 0 with pirq 4f gvec 59
pt_msixctrl_reg_write: guest enabling MSI-X, disable MSI-INTx translation
pci_intx: intx=1
pt_msi_disable: Unmap msi with pirq 4e
pt_msix_update_one: Update msix entry 0 with pirq 4e gvec 69
pci_msix_writel: Can't update entry 0 since MSI-X is already enabled 
(fee00000 -> fee02000)
pci_msix_writel: Can't update entry 0 since MSI-X is already enabled 
(00004059 -> 00004071)

Can't reproduce with uek2(3.1 stable), but if I disable hvm_pirqs 
support in uek2, reproduce the same.
Test patch below:
diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
index a22ad4b..2d795d1 100644
--- a/arch/x86/pci/xen.c
+++ b/arch/x86/pci/xen.c
@-400,7 +400,6 @int __init pci_xen_init(void)
.
 int __init pci_xen_hvm_init(void)
 {
-       if (!xen_have_vector_callback || !xen_feature(XENFEAT_hvm_pirqs))
                return 0;
.
 #ifdef CONFIG_ACPI
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index bf28d69..64f6c6c 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@-1536,8 +1536,6 @bool xen_hvm_need_lapic(void)
                return false;
        if (!xen_hvm_domain())
                return false;
-       if (xen_feature(XENFEAT_hvm_pirqs) && xen_have_vector_callback)
-               return false;
        return true;
 }
 EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);

btw: can't reproduce too if disable msi support.
I'll upload what you need, just tell me.

thanks
zduan