Re: [Qemu-devel] [PATCH qemu v7 4/4] ppc/spapr, vfio: Turn off MSIX emulation for VFIO devices

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Feb 09, 2018 at 06:55:03PM +1100, Alexey Kardashevskiy wrote:
> This adds a possibility for the platform to tell VFIO not to emulate MSIX
> so MMIO memory regions do not get split into chunks in flatview and
> the entire page can be registered as a KVM memory slot and make direct
> MMIO access possible for the guest.
> 
> This enables the entire MSIX BAR mapping to the guest for the pseries
> platform in order to achieve the maximum MMIO preformance for certain
> devices.
> 
> Tested on:
> LSI Logic / Symbios Logic SAS3008 PCI-Express Fusion-MPT SAS-3 (rev 02)
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

I still think having the property on the machine is an uglier option
than having it on the device, but Alex didn't like that, so I'll roll
with it.

Reivewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> 
> Need to split this in two?
> ---
>  hw/ppc/spapr.c |  7 +++++++
>  hw/vfio/pci.c  | 13 +++++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index eb3e1a7..14d8ecb 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2855,6 +2855,11 @@ static void spapr_set_modern_hotplug_events(Object *obj, bool value,
>      spapr->use_hotplug_event_source = value;
>  }
>  
> +static bool spapr_get_msix_emulation(Object *obj, Error **errp)
> +{
> +    return true;
> +}
> +
>  static char *spapr_get_resize_hpt(Object *obj, Error **errp)
>  {
>      sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
> @@ -2936,6 +2941,8 @@ static void spapr_instance_init(Object *obj)
>      object_property_set_description(obj, "vsmt",
>                                      "Virtual SMT: KVM behaves as if this were"
>                                      " the host's SMT mode", &error_abort);
> +    object_property_add_bool(obj, "vfio-no-msix-emulation",
> +                             spapr_get_msix_emulation, NULL, NULL);
>  }
>  
>  static void spapr_machine_finalizefn(Object *obj)
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index ae9098d..4a03085 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -1580,6 +1580,19 @@ static int vfio_msix_setup(VFIOPCIDevice *vdev, int pos, Error **errp)
>       */
>      memory_region_set_enabled(&vdev->pdev.msix_pba_mmio, false);
>  
> +    /*
> +     * The emulated machine may provide a paravirt interface for MSIX setup
> +     * so it is not strictly necessary to emulate MSIX here. This becomes
> +     * helpful when frequently accessed MMIO registers are located in
> +     * subpages adjacent to the MSIX table but the MSIX data containing page
> +     * cannot be mapped because of a host page size bigger than the MSIX table
> +     * alignment.
> +     */
> +    if (object_property_get_bool(OBJECT(qdev_get_machine()),
> +                                 "vfio-no-msix-emulation", NULL)) {
> +        memory_region_set_enabled(&vdev->pdev.msix_table_mmio, false);
> +    }
> +
>      return 0;
>  }
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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