[PATCH RFC 4/4] xen/pvhvm: Make MSI IRQs work after kexec

[Vitaly Kuznetsov <vkuznets@redhat.com>]

When kexec was peformed MSI IRQs for passthrough-ed devices were already
mapped and we see non-zero pirq extracted from MSI msg. xen_irq_from_pirq()
fails as we have no IRQ mapping information for that. Requesting for new
mapping with __write_msi_msg() does not result in MSI IRQ being remapped so
we don't recieve these IRQs.

RFC: I wasn't able to understand why commit af42b8d1 which introduced
xen_irq_from_pirq() check in xen_hvm_setup_msi_irqs() is checking that instead
of checking pirq > 0 as if the mapping was already done (and we have pirq>0 here)
we don't need to request for a new pirq. We're loosing existing PIRQ and I'm also
not sure when __write_msi_msg() with new PIRQ will result in new mapping.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/pci/xen.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
index 905956f..685e8f1 100644
--- a/arch/x86/pci/xen.c
+++ b/arch/x86/pci/xen.c
@@ -231,8 +231,7 @@ static int xen_hvm_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
 		__read_msi_msg(msidesc, &msg);
 		pirq = MSI_ADDR_EXT_DEST_ID(msg.address_hi) |
 			((msg.address_lo >> MSI_ADDR_DEST_ID_SHIFT) & 0xff);
-		if (msg.data != XEN_PIRQ_MSI_DATA ||
-		    xen_irq_from_pirq(pirq) < 0) {
+		if (msg.data != XEN_PIRQ_MSI_DATA || pirq <= 0) {
 			pirq = xen_allocate_pirq_msi(dev, msidesc);
 			if (pirq < 0) {
 				irq = -ENODEV;
-- 
1.9.3