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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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? 
> 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?
> 
> 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?
> +                     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?

> +                             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?
> +                     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 6e5dd92..5de6a6c 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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