RE: [PATCH for-4.14 v2 2/2] x86/passthrough: introduce a flag for GSIs not requiring an EOI or unmask

[Paul Durrant <xadimgnik@gmail.com>]

> -----Original Message-----
> From: Roger Pau Monne <roger.pau@citrix.com>
> Sent: 10 June 2020 15:29
> To: xen-devel@lists.xenproject.org
> Cc: paul@xen.org; Roger Pau Monne <roger.pau@citrix.com>; Jan Beulich <jbeulich@suse.com>; Andrew
> Cooper <andrew.cooper3@citrix.com>; Wei Liu <wl@xen.org>
> Subject: [PATCH for-4.14 v2 2/2] x86/passthrough: introduce a flag for GSIs not requiring an EOI or
> unmask
> 
> There's no need to setup a timer for GSIs that are edge triggered,
> since those don't require any EIO or unmask, and hence couldn't block
> other interrupts.
> 
> Note this is only used by PVH dom0, that can setup the passthrough of
> edge triggered interrupts from the vIO-APIC. One example of such kind
> of interrupt that can be used by a PVH dom0 would be the RTC timer.
> 
> While there introduce an out label to do the unlock and reduce code
> duplication.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>

Reviewed-by: Paul Durrant <paul@xen.org>

> ---
> Changes since v1:
>  - Introduce an out label that does the unlock.
> ---
>  xen/drivers/passthrough/io.c  | 24 +++++++++++++++---------
>  xen/include/asm-x86/hvm/irq.h |  2 ++
>  2 files changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/xen/drivers/passthrough/io.c b/xen/drivers/passthrough/io.c
> index b292e79382..6b1305a3e5 100644
> --- a/xen/drivers/passthrough/io.c
> +++ b/xen/drivers/passthrough/io.c
> @@ -138,7 +138,8 @@ static void pt_pirq_softirq_reset(struct hvm_pirq_dpci *pirq_dpci)
> 
>  bool pt_irq_need_timer(uint32_t flags)
>  {
> -    return !(flags & (HVM_IRQ_DPCI_GUEST_MSI | HVM_IRQ_DPCI_TRANSLATE));
> +    return !(flags & (HVM_IRQ_DPCI_GUEST_MSI | HVM_IRQ_DPCI_TRANSLATE |
> +                      HVM_IRQ_DPCI_NO_EOI));
>  }
> 
>  static int pt_irq_guest_eoi(struct domain *d, struct hvm_pirq_dpci *pirq_dpci,
> @@ -558,6 +559,12 @@ int pt_irq_create_bind(
>                       */
>                      ASSERT(!mask);
>                      share = trigger_mode;
> +                    if ( trigger_mode == VIOAPIC_EDGE_TRIG )
> +                        /*
> +                         * Edge IO-APIC interrupt, no EOI or unmask to perform
> +                         * and hence no timer needed.
> +                         */
> +                        pirq_dpci->flags |= HVM_IRQ_DPCI_NO_EOI;
>                  }
>              }
> 
> @@ -897,17 +904,13 @@ static void hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci)
>              send_guest_pirq(d, pirq);
> 
>              if ( pirq_dpci->flags & HVM_IRQ_DPCI_GUEST_MSI )
> -            {
> -                spin_unlock(&d->event_lock);
> -                return;
> -            }
> +                goto out;
>          }
> 
>          if ( pirq_dpci->flags & HVM_IRQ_DPCI_GUEST_MSI )
>          {
>              vmsi_deliver_pirq(d, pirq_dpci);
> -            spin_unlock(&d->event_lock);
> -            return;
> +            goto out;
>          }
> 
>          list_for_each_entry ( digl, &pirq_dpci->digl_list, list )
> @@ -920,6 +923,8 @@ static void hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci)
>          if ( pirq_dpci->flags & HVM_IRQ_DPCI_IDENTITY_GSI )
>          {
>              hvm_gsi_assert(d, pirq->pirq);
> +            if ( pirq_dpci->flags & HVM_IRQ_DPCI_NO_EOI )
> +                goto out;
>              pirq_dpci->pending++;
>          }
> 
> @@ -927,8 +932,7 @@ static void hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci)
>          {
>              /* for translated MSI to INTx interrupt, eoi as early as possible */
>              __msi_pirq_eoi(pirq_dpci);
> -            spin_unlock(&d->event_lock);
> -            return;
> +            goto out;
>          }
> 
>          /*
> @@ -941,6 +945,8 @@ static void hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci)
>          ASSERT(pt_irq_need_timer(pirq_dpci->flags));
>          set_timer(&pirq_dpci->timer, NOW() + PT_IRQ_TIME_OUT);
>      }
> +
> + out:
>      spin_unlock(&d->event_lock);
>  }
> 
> diff --git a/xen/include/asm-x86/hvm/irq.h b/xen/include/asm-x86/hvm/irq.h
> index d306cfeade..532880d497 100644
> --- a/xen/include/asm-x86/hvm/irq.h
> +++ b/xen/include/asm-x86/hvm/irq.h
> @@ -121,6 +121,7 @@ struct dev_intx_gsi_link {
>  #define _HVM_IRQ_DPCI_GUEST_PCI_SHIFT           4
>  #define _HVM_IRQ_DPCI_GUEST_MSI_SHIFT           5
>  #define _HVM_IRQ_DPCI_IDENTITY_GSI_SHIFT        6
> +#define _HVM_IRQ_DPCI_NO_EOI_SHIFT              7
>  #define _HVM_IRQ_DPCI_TRANSLATE_SHIFT          15
>  #define HVM_IRQ_DPCI_MACH_PCI        (1u << _HVM_IRQ_DPCI_MACH_PCI_SHIFT)
>  #define HVM_IRQ_DPCI_MACH_MSI        (1u << _HVM_IRQ_DPCI_MACH_MSI_SHIFT)
> @@ -129,6 +130,7 @@ struct dev_intx_gsi_link {
>  #define HVM_IRQ_DPCI_GUEST_PCI       (1u << _HVM_IRQ_DPCI_GUEST_PCI_SHIFT)
>  #define HVM_IRQ_DPCI_GUEST_MSI       (1u << _HVM_IRQ_DPCI_GUEST_MSI_SHIFT)
>  #define HVM_IRQ_DPCI_IDENTITY_GSI    (1u << _HVM_IRQ_DPCI_IDENTITY_GSI_SHIFT)
> +#define HVM_IRQ_DPCI_NO_EOI          (1u << _HVM_IRQ_DPCI_NO_EOI_SHIFT)
>  #define HVM_IRQ_DPCI_TRANSLATE       (1u << _HVM_IRQ_DPCI_TRANSLATE_SHIFT)
> 
>  struct hvm_gmsi_info {
> --
> 2.26.2