Re: [v3 11/15] Update IRTE according to guest interrupt config changes

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 24/06/15 06:18, Feng Wu wrote:
> When guest changes its interrupt configuration (such as, vector, etc.)
> for direct-assigned devices, we need to update the associated IRTE
> with the new guest vector, so external interrupts from the assigned
> devices can be injected to guests without VM-Exit.
>
> For lowest-priority interrupts, we use vector-hashing mechamisn to find
> the destination vCPU. This follows the hardware behavior, since modern
> Intel CPUs use vector hashing to handle the lowest-priority interrupt.
>
> For multicast/broadcast vCPU, we cannot handle it via interrupt posting,
> still use interrupt remapping.
>
> Signed-off-by: Feng Wu <feng.wu@intel.com>
> ---
> v3:
> - Use bitmap to store the all the possible destination vCPUs of an
> interrupt, then trying to find the right destination from the bitmap
> - Typo and some small changes
>
>  xen/drivers/passthrough/io.c | 96 +++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 95 insertions(+), 1 deletion(-)
>
> diff --git a/xen/drivers/passthrough/io.c b/xen/drivers/passthrough/io.c
> index 9b77334..18e24e1 100644
> --- a/xen/drivers/passthrough/io.c
> +++ b/xen/drivers/passthrough/io.c
> @@ -26,6 +26,7 @@
>  #include <asm/hvm/iommu.h>
>  #include <asm/hvm/support.h>
>  #include <xen/hvm/irq.h>
> +#include <asm/io_apic.h>
>  
>  static DEFINE_PER_CPU(struct list_head, dpci_list);
>  
> @@ -199,6 +200,78 @@ void free_hvm_irq_dpci(struct hvm_irq_dpci *dpci)
>      xfree(dpci);
>  }
>  
> +/*
> + * The purpose of this routine is to find the right destination vCPU for
> + * an interrupt which will be delivered by VT-d posted-interrupt. There
> + * are several cases as below:
> + *
> + * - For lowest-priority interrupts, we find the destination vCPU from the
> + *   guest vector using vector-hashing mechanism and return true. This follows
> + *   the hardware behavior, since modern Intel CPUs use vector hashing to
> + *   handle the lowest-priority interrupt.
> + * - Otherwise, for single destination interrupt, it is straightforward to
> + *   find the destination vCPU and return true.
> + * - For multicast/broadcast vCPU, we cannot handle it via interrupt posting,
> + *   so return false.

s/false/NULL/ ?

> + *
> + *   Here is the details about the vector-hashing mechanism:
> + *   1. For lowest-priority interrupts, store all the possible destination
> + *      vCPUs in an array.
> + *   2. Use "gvec % max number of destination vCPUs" to find the right
> + *      destination vCPU in the array for the lowest-priority interrupt.
> + */
> +static struct vcpu *pi_find_dest_vcpu(struct domain *d, uint8_t dest_id,

dest_id should clearly be 32bits rather than 8.

> +                                      uint8_t dest_mode, uint8_t delivery_mode,
> +                                      uint8_t gvec)
> +{
> +    unsigned long *dest_vcpu_bitmap = NULL;
> +    unsigned int dest_vcpu_num = 0, idx = 0;
> +    int size = (d->max_vcpus + BITS_PER_LONG - 1) / BITS_PER_LONG;

unsigned int, and "size" is far too generic of a name.

> +    struct vcpu *v, *dest = NULL;
> +    int i;

Also unsigned.

> +
> +    dest_vcpu_bitmap = xzalloc_array(unsigned long, size);
> +    if ( !dest_vcpu_bitmap )
> +    {
> +        dprintk(XENLOG_G_INFO,
> +                "dom%d: failed to allocate memory\n", d->domain_id);
> +        return NULL;
> +    }
> +
> +    for_each_vcpu ( d, v )
> +    {
> +        if ( !vlapic_match_dest(vcpu_vlapic(v), NULL, 0,
> +                                dest_id, dest_mode) )
> +            continue;
> +
> +        __set_bit(v->vcpu_id, dest_vcpu_bitmap);
> +        dest_vcpu_num++;
> +    }
> +
> +    if ( delivery_mode == dest_LowestPrio )
> +    {
> +        if (  dest_vcpu_num != 0 )

Too many spaces inside the brackets.

> +        {
> +            for ( i = 0; i <= gvec % dest_vcpu_num; i++)
> +                idx = find_next_bit(dest_vcpu_bitmap, d->max_vcpus, idx) + 1;
> +            idx--;
> +
> +            BUG_ON(idx >= d->max_vcpus || idx < 0);
> +            dest = d->vcpu[idx];
> +        }
> +    }
> +    else if (  dest_vcpu_num == 1 )
> +    {
> +        idx = find_first_bit(dest_vcpu_bitmap, d->max_vcpus);
> +        BUG_ON(idx >= d->max_vcpus || idx < 0);

find_first_bit() is unsigned, so can never be less than 0.

> +        dest = d->vcpu[idx];
> +    }
> +
> +    xfree(dest_vcpu_bitmap);
> +
> +    return dest;
> +}
> +
>  int pt_irq_create_bind(
>      struct domain *d, xen_domctl_bind_pt_irq_t *pt_irq_bind)
>  {
> @@ -257,7 +330,7 @@ int pt_irq_create_bind(
>      {
>      case PT_IRQ_TYPE_MSI:
>      {
> -        uint8_t dest, dest_mode;
> +        uint8_t dest, dest_mode, delivery_mode;
>          int dest_vcpu_id;
>  
>          if ( !(pirq_dpci->flags & HVM_IRQ_DPCI_MAPPED) )
> @@ -330,11 +403,32 @@ int pt_irq_create_bind(
>          /* Calculate dest_vcpu_id for MSI-type pirq migration. */
>          dest = pirq_dpci->gmsi.gflags & VMSI_DEST_ID_MASK;
>          dest_mode = !!(pirq_dpci->gmsi.gflags & VMSI_DM_MASK);
> +        delivery_mode = (pirq_dpci->gmsi.gflags >> GFLAGS_SHIFT_DELIV_MODE) &
> +                        VMSI_DELIV_MASK;
>          dest_vcpu_id = hvm_girq_dest_2_vcpu_id(d, dest, dest_mode);
>          pirq_dpci->gmsi.dest_vcpu_id = dest_vcpu_id;
>          spin_unlock(&d->event_lock);
>          if ( dest_vcpu_id >= 0 )
>              hvm_migrate_pirqs(d->vcpu[dest_vcpu_id]);
> +
> +        /* Use interrupt posting if it is supported */
> +        if ( iommu_intpost )
> +        {
> +            struct vcpu *vcpu = pi_find_dest_vcpu(d, dest, dest_mode,
> +                                        delivery_mode, pirq_dpci->gmsi.gvec);
> +
> +            if ( !vcpu )
> +                dprintk(XENLOG_G_WARNING,
> +                        "dom%u: failed to find the dest vCPU for PI, guest "
> +                        "vector:0x%x use software way to deliver the "
> +                        " interrupts.\n", d->domain_id, pirq_dpci->gmsi.gvec);

If this is normal for a multicast interrupt, it must not be a WARNING
level error message.  It probably shouldn't even be a message at all.

~Andrew

> +            else if ( pi_update_irte( vcpu, info, pirq_dpci->gmsi.gvec ) != 0 )
> +                dprintk(XENLOG_G_WARNING,
> +                        "%pv: failed to update PI IRTE, guest vector:0x%x "
> +                        "use software way to deliver the interrupts.\n",
> +                        vcpu, pirq_dpci->gmsi.gvec);
> +        }
> +
>          break;
>      }
>