[Xen-devel] Re: [PATCH] xen: fix MSI setup and teardown for PV on HVM guests

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 29 Nov 2010, Konrad Rzeszutek Wilk wrote:
> On Fri, Nov 26, 2010 at 02:59:10PM +0000, Stefano Stabellini wrote:
> > xen: fix MSI setup and teardown for PV on HVM guests
> > 
> > When remapping MSIs into pirqs for PV on HVM guests, qemu is responsible
> > for doing the actual mapping and unmapping.
> 
> Is this QEMU version dependent? 

It depends on both qemu and xen: the presence of this feature (pirq
remapping for hvm guests) is signaled by the flag
XENFEAT_hvm_pirqs that we check in pci_xen_hvm_init.


> > We only give qemu the desired pirq number when we ask to do the mapping
> > the first time, after that we should be reading back the pirq number
> > from qemu every time we want to re-enable the MSI.
> 
> What about IRQ migration from CPU to CPU?

that should follow the normal pirq/evtchn migration code paths in
drivers/xen/event.c


> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > 
> > diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
> > index d7b5109..ff81d67 100644
> > --- a/arch/x86/pci/xen.c
> > +++ b/arch/x86/pci/xen.c
> > @@ -98,8 +98,26 @@ static int xen_hvm_setup_msi_irqs(struct pci_dev *dev, 
> > int nvec, int type)
> >     struct msi_msg msg;
> >  
> >     list_for_each_entry(msidesc, &dev->msi_list, list) {
> > +           __read_msi_msg(msidesc, &msg);
> > +           pirq = MSI_ADDR_EXT_DEST_ID(msg.address_hi) |
> > +                   ((msg.address_lo >> MSI_ADDR_DEST_ID_SHIFT) & 0xff);
> > +           if (xen_irq_from_pirq(pirq) >= 0 &&
> > +                   msg.data == (MSI_DATA_TRIGGER_EDGE |
> > +                                        MSI_DATA_LEVEL_ASSERT |
> > +                                            (3 << 8) |
> > +                                            MSI_DATA_VECTOR(0))) {
> 
> A similar construct is used in xen_msi_compose_msg function. Could you
> make this an #define?

yes, good idea.


> > +                   xen_allocate_pirq_msi((type == PCI_CAP_ID_MSIX) ?
> > +                                   "msi-x" : "msi", &irq, &pirq, 
> > XEN_ALLOC_IRQ);
> > +                   if (irq < 0 || pirq < 0)
> 
> The pirq value won't be touched at all, since you are passing in 
> XEN_ALLOC_IRQ.
> Is there any sense in checking the pirq value here?
> 

not really, just legacy. I'll fix it.


> > +                           goto error;
> > +                   ret = set_irq_msi(irq, msidesc);
> > +                   if (ret < 0)
> > +                           goto error_while;
> > +                   printk(KERN_DEBUG "xen: msi already setup: pirq=%d\n", 
> > pirq);
> 
> While that is technically correct, would it make sense to add a comment
> about setting the IRQ value since the printk "xen: msi-->irq=%d" is not going
> to be reached?

you mean printing the irq value as well? Sure.

---


diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
index d7b5109..25cd4a0 100644
--- a/arch/x86/pci/xen.c
+++ b/arch/x86/pci/xen.c
@@ -70,6 +70,9 @@ static int acpi_register_gsi_xen_hvm(struct device *dev, u32 
gsi,
 struct xen_pci_frontend_ops *xen_pci_frontend;
 EXPORT_SYMBOL_GPL(xen_pci_frontend);
 
+#define XEN_PIRQ_MSI_DATA  (MSI_DATA_TRIGGER_EDGE | \
+               MSI_DATA_LEVEL_ASSERT | (3 << 8) | MSI_DATA_VECTOR(0))
+
 static void xen_msi_compose_msg(struct pci_dev *pdev, unsigned int pirq,
                struct msi_msg *msg)
 {
@@ -83,12 +86,7 @@ static void xen_msi_compose_msg(struct pci_dev *pdev, 
unsigned int pirq,
                MSI_ADDR_REDIRECTION_CPU |
                MSI_ADDR_DEST_ID(pirq);
 
-       msg->data =
-               MSI_DATA_TRIGGER_EDGE |
-               MSI_DATA_LEVEL_ASSERT |
-               /* delivery mode reserved */
-               (3 << 8) |
-               MSI_DATA_VECTOR(0);
+       msg->data = XEN_PIRQ_MSI_DATA;
 }
 
 static int xen_hvm_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
@@ -98,8 +96,23 @@ static int xen_hvm_setup_msi_irqs(struct pci_dev *dev, int 
nvec, int type)
        struct msi_msg msg;
 
        list_for_each_entry(msidesc, &dev->msi_list, list) {
+               __read_msi_msg(msidesc, &msg);
+               pirq = MSI_ADDR_EXT_DEST_ID(msg.address_hi) |
+                       ((msg.address_lo >> MSI_ADDR_DEST_ID_SHIFT) & 0xff);
+               if (xen_irq_from_pirq(pirq) >= 0 && msg.data == 
XEN_PIRQ_MSI_DATA) {
+                       xen_allocate_pirq_msi((type == PCI_CAP_ID_MSIX) ?
+                                       "msi-x" : "msi", &irq, &pirq, 
XEN_ALLOC_IRQ);
+                       if (irq < 0)
+                               goto error;
+                       ret = set_irq_msi(irq, msidesc);
+                       if (ret < 0)
+                               goto error_while;
+                       printk(KERN_DEBUG "xen: msi already setup: msi --> 
irq=%d"
+                                       " pirq=%d\n", irq, pirq);
+                       return 0;
+               }
                xen_allocate_pirq_msi((type == PCI_CAP_ID_MSIX) ?
-                               "msi-x" : "msi", &irq, &pirq);
+                               "msi-x" : "msi", &irq, &pirq, (XEN_ALLOC_IRQ | 
XEN_ALLOC_PIRQ));
                if (irq < 0 || pirq < 0)
                        goto error;
                printk(KERN_DEBUG "xen: msi --> irq=%d, pirq=%d\n", irq, pirq);
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 7ab43c3..f78945c 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -668,17 +668,21 @@ out:
 #include <linux/msi.h>
 #include "../pci/msi.h"
 
-void xen_allocate_pirq_msi(char *name, int *irq, int *pirq)
+void xen_allocate_pirq_msi(char *name, int *irq, int *pirq, int alloc)
 {
        spin_lock(&irq_mapping_update_lock);
 
-       *irq = find_unbound_irq();
-       if (*irq == -1)
-               goto out;
+       if (alloc & XEN_ALLOC_IRQ) {
+               *irq = find_unbound_irq();
+               if (*irq == -1)
+                       goto out;
+       }
 
-       *pirq = find_unbound_pirq(MAP_PIRQ_TYPE_MSI);
-       if (*pirq == -1)
-               goto out;
+       if (alloc & XEN_ALLOC_PIRQ) {
+               *pirq = find_unbound_pirq(MAP_PIRQ_TYPE_MSI);
+               if (*pirq == -1)
+                       goto out;
+       }
 
        set_irq_chip_and_handler_name(*irq, &xen_pirq_chip,
                                      handle_level_irq, name);
@@ -766,6 +770,7 @@ int xen_destroy_irq(int irq)
                        printk(KERN_WARNING "unmap irq failed %d\n", rc);
                        goto out;
                }
+               pirq_to_irq[info->u.pirq.pirq] = -1;
        }
        irq_info[irq] = mk_unbound_info();
 
@@ -786,6 +791,11 @@ int xen_gsi_from_irq(unsigned irq)
        return gsi_from_irq(irq);
 }
 
+int xen_irq_from_pirq(unsigned pirq)
+{
+       return pirq_to_irq[pirq];
+}
+
 int bind_evtchn_to_irq(unsigned int evtchn)
 {
        int irq;
diff --git a/include/xen/events.h b/include/xen/events.h
index 646dd17..00f53dd 100644
--- a/include/xen/events.h
+++ b/include/xen/events.h
@@ -76,7 +76,9 @@ int xen_map_pirq_gsi(unsigned pirq, unsigned gsi, int 
shareable, char *name);
 
 #ifdef CONFIG_PCI_MSI
 /* Allocate an irq and a pirq to be used with MSIs. */
-void xen_allocate_pirq_msi(char *name, int *irq, int *pirq);
+#define XEN_ALLOC_PIRQ (1 << 0)
+#define XEN_ALLOC_IRQ  (1 << 1)
+void xen_allocate_pirq_msi(char *name, int *irq, int *pirq, int alloc_mask);
 int xen_create_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc, int 
type);
 #endif
 
@@ -89,4 +91,7 @@ int xen_vector_from_irq(unsigned pirq);
 /* Return gsi allocated to pirq */
 int xen_gsi_from_irq(unsigned pirq);
 
+/* Return irq from pirq */
+int xen_irq_from_pirq(unsigned pirq);
+
 #endif /* _XEN_EVENTS_H */

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