[RFC KERNEL PATCH v2 2/3] xen/pvh: Unmask irq for passthrough device in PVH dom0

[Jiqian Chen <Jiqian.Chen@xxxxxxx>]

This patch is to solve two problems we encountered when we try to
passthrough a device to hvm domU base on Xen PVH dom0.

First, hvm guest will alloc a pirq and irq for a passthrough device
by using gsi, before that, the gsi must first has a mapping in dom0,
see Xen code pci_add_dm_done->xc_domain_irq_permission, it will call
into Xen and check whether dom0 has the mapping. See
XEN_DOMCTL_irq_permission->pirq_access_permitted, "current" is PVH
dom0 and it return irq is 0, and then return -EPERM.
This is because the passthrough device doesn't do PHYSDEVOP_map_pirq
when thay are enabled.

Second, in PVH dom0, the gsi of a passthrough device doesn't get
registered, but gsi must be configured for it to be able to be
mapped into a domU.

After searching codes, we can find map_pirq and register_gsi will be
done in function vioapic_write_redirent->vioapic_hwdom_map_gsi when
the gsi(aka ioapic's pin) is unmasked in PVH dom0. So the problems
can be conclude to that the gsi of a passthrough device doesn't be
unmasked.

To solve the unmaske problem, this patch call the unmask_irq when we
assign a device to be passthrough. So that the gsi can get registered
and mapped in PVH dom0.

Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
---
 drivers/xen/xen-pciback/pci_stub.c | 7 +++++++
 include/linux/irq.h                | 1 +
 kernel/irq/chip.c                  | 1 +
 kernel/irq/internals.h             | 1 -
 kernel/irq/irqdesc.c               | 2 +-
 5 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/xen-pciback/pci_stub.c 
b/drivers/xen/xen-pciback/pci_stub.c
index 5a96b6c66c07..b83d02bcc76c 100644
--- a/drivers/xen/xen-pciback/pci_stub.c
+++ b/drivers/xen/xen-pciback/pci_stub.c
@@ -357,6 +357,7 @@ static int pcistub_match(struct pci_dev *dev)
 static int pcistub_init_device(struct pci_dev *dev)
 {
        struct xen_pcibk_dev_data *dev_data;
+       struct irq_desc *desc = NULL;
        int err = 0;
 
        dev_dbg(&dev->dev, "initializing...\n");
@@ -399,6 +400,12 @@ static int pcistub_init_device(struct pci_dev *dev)
        if (err)
                goto config_release;
 
+       if (xen_initial_domain() && xen_pvh_domain()) {
+               if (dev->irq <= 0 || !(desc = irq_to_desc(dev->irq)))
+                       goto config_release;
+               unmask_irq(desc);
+       }
+
        if (dev->msix_cap) {
                struct physdev_pci_device ppdev = {
                        .seg = pci_domain_nr(dev->bus),
diff --git a/include/linux/irq.h b/include/linux/irq.h
index 90081afa10ce..44650ca178d9 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -659,6 +659,7 @@ extern void handle_percpu_irq(struct irq_desc *desc);
 extern void handle_percpu_devid_irq(struct irq_desc *desc);
 extern void handle_bad_irq(struct irq_desc *desc);
 extern void handle_nested_irq(unsigned int irq);
+extern void unmask_irq(struct irq_desc *desc);
 
 extern void handle_fasteoi_nmi(struct irq_desc *desc);
 extern void handle_percpu_devid_fasteoi_nmi(struct irq_desc *desc);
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index dc94e0bf2c94..fd67b40b678d 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -439,6 +439,7 @@ void unmask_irq(struct irq_desc *desc)
                irq_state_clr_masked(desc);
        }
 }
+EXPORT_SYMBOL_GPL(unmask_irq);
 
 void unmask_threaded_irq(struct irq_desc *desc)
 {
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index bcc7f21db9ee..d08e3e7b2819 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -95,7 +95,6 @@ extern void irq_disable(struct irq_desc *desc);
 extern void irq_percpu_enable(struct irq_desc *desc, unsigned int cpu);
 extern void irq_percpu_disable(struct irq_desc *desc, unsigned int cpu);
 extern void mask_irq(struct irq_desc *desc);
-extern void unmask_irq(struct irq_desc *desc);
 extern void unmask_threaded_irq(struct irq_desc *desc);
 
 #ifdef CONFIG_SPARSE_IRQ
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 27ca1c866f29..5977efed31b5 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -380,7 +380,7 @@ struct irq_desc *irq_to_desc(unsigned int irq)
 {
        return mtree_load(&sparse_irqs, irq);
 }
-#ifdef CONFIG_KVM_BOOK3S_64_HV_MODULE
+#if defined CONFIG_KVM_BOOK3S_64_HV_MODULE || defined CONFIG_XEN_PVH
 EXPORT_SYMBOL_GPL(irq_to_desc);
 #endif
 
-- 
2.34.1