Re: [Qemu-devel] [PATCH qemu v2] RFC: vfio-pci: Allow mmap of MSIX BAR

[David Gibson]

On Fri, Dec 15, 2017 at 05:29:14PM +1100, Alexey Kardashevskiy wrote:
> This makes use of a new VFIO_REGION_INFO_CAP_MSIX_MAPPABLE capability
> which tells that a region with MSIX data can be mapped entirely, i.e.
> the VFIO PCI driver won't prevent MSIX vectors area from being mapped.
> 
> With this change, all BARs are mapped in a single chunk and MSIX vectors
> are emulated on top unless the machine requests not to by defining and
> enabling a new "vfio-no-msix-emulation" property. At the moment only
> sPAPR machine does so - it prohibits MSIX emulation and does not allow
> enabling it as it does not define the "set" callback for the new property;
> the new property also does not appear in "-machine pseries,help".
> 
> If the new capability is present, this puts MSIX IO memory region under
> mapped memory region. If the capability is not there, it falls back to
> the old behaviour with the sparse capability.
> 
> In MSIX vectors section is not aligned to the page size, the KVM memory
> listener does not register it with the KVM as a memory slot and MSIX is
> emulated by QEMU as before.
> 
> This requires the kernel change - "vfio-pci: Allow mapping MSIX BAR" -
> for the new capability: https://www.spinics.net/lists/kvm/msg160282.html
> 
> Signed-off-by: Alexey Kardashevskiy <address@hidden>
> ---
> 
> This is mtree and flatview BEFORE this patch:
> 
> "info mtree":
> memory-region: address@hidden
>   0000000000000000-ffffffffffffffff (prio 0, i/o): address@hidden
>     0000210000000000-000021000000ffff (prio 1, i/o): 0001:03:00.0 BAR 1
>       000021000000e000-000021000000e5ff (prio 0, i/o): msix-table
>       000021000000f000-000021000000f00f (prio 0, i/o): msix-pba [disabled]
>     0000210000040000-000021000007ffff (prio 1, i/o): 0001:03:00.0 BAR 3
>       0000210000040000-000021000007ffff (prio 0, ramd): 0001:03:00.0 BAR 3 
> mmaps[0]
> 
> "info mtree -f":
> FlatView #0
>  AS "memory", root: system
>  AS "cpu-memory", root: system
>  Root memory region: system
>   0000000000000000-000000007fffffff (prio 0, ram): ppc_spapr.ram
>   0000210000000000-000021000000dfff (prio 1, i/o): 0001:03:00.0 BAR 1
>   000021000000e000-000021000000e5ff (prio 0, i/o): msix-table
>   000021000000e600-000021000000ffff (prio 1, i/o): 0001:03:00.0 BAR 1 
> @000000000000e600
>   0000210000040000-000021000007ffff (prio 0, ramd): 0001:03:00.0 BAR 3 
> mmaps[0]
> 
> 
> 
> This is AFTER this patch applied:
> 
> "info mtree":
> memory-region: address@hidden
>   0000000000000000-ffffffffffffffff (prio 0, i/o): address@hidden
>     0000210000000000-000021000000ffff (prio 1, i/o): 0001:03:00.0 BAR 1
>       0000210000000000-000021000000ffff (prio 0, ramd): 0001:03:00.0 BAR 1 
> mmaps[0]
>         000021000000e000-000021000000e5ff (prio 0, i/o): msix-table [disabled]
>         000021000000f000-000021000000f00f (prio 0, i/o): msix-pba [disabled]
>     0000210000040000-000021000007ffff (prio 1, i/o): 0001:03:00.0 BAR 3
>       0000210000040000-000021000007ffff (prio 0, ramd): 0001:03:00.0 BAR 3 
> mmaps[0]
> 
> 
> "info mtree -f":
> FlatView #2
>  AS "memory", root: system
>  AS "cpu-memory", root: system
>  Root memory region: system
>   0000000000000000-000000007fffffff (prio 0, ram): ppc_spapr.ram
>   0000210000000000-000021000000ffff (prio 0, ramd): 0001:03:00.0 BAR 1 
> mmaps[0]
>   0000210000040000-000021000007ffff (prio 0, ramd): 0001:03:00.0 BAR 3 
> mmaps[0]
> 
> 
> 
> This is AFTER this patch applied AND spapr_get_msix_emulation() patched
> to enable emulation:
> 
> "info mtree":
> memory-region: address@hidden
>   0000000000000000-ffffffffffffffff (prio 0, i/o): address@hidden
>     0000210000000000-000021000000ffff (prio 1, i/o): 0001:03:00.0 BAR 1
>       0000210000000000-000021000000ffff (prio 0, ramd): 0001:03:00.0 BAR 1 
> mmaps[0]
>         000021000000e000-000021000000e5ff (prio 0, i/o): msix-table
>         000021000000f000-000021000000f00f (prio 0, i/o): msix-pba [disabled]
>     0000210000040000-000021000007ffff (prio 1, i/o): 0001:03:00.0 BAR 3
>       0000210000040000-000021000007ffff (prio 0, ramd): 0001:03:00.0 BAR 3 
> mmaps[0]
> 
> "info mtree -f":
> FlatView #1
>  AS "memory", root: system
>  AS "cpu-memory", root: system
>  Root memory region: system
>   0000000000000000-000000007fffffff (prio 0, ram): ppc_spapr.ram
>   0000210000000000-000021000000dfff (prio 0, ramd): 0001:03:00.0 BAR 1 
> mmaps[0]
>   000021000000e000-000021000000e5ff (prio 0, i/o): msix-table
>   000021000000e600-000021000000ffff (prio 0, ramd): 0001:03:00.0 BAR 1 
> mmaps[0] @000000000000e600
>   0000210000040000-000021000007ffff (prio 0, ramd): 0001:03:00.0 BAR 3 
> mmaps[0]
> ---
>  include/hw/vfio/vfio-common.h |  1 +
>  linux-headers/linux/vfio.h    |  5 +++++
>  hw/ppc/spapr.c                |  8 ++++++++
>  hw/vfio/common.c              | 15 +++++++++++++++
>  hw/vfio/pci.c                 | 23 +++++++++++++++++++++--
>  5 files changed, 50 insertions(+), 2 deletions(-)
> 
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index f3a2ac9..927d600 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -171,6 +171,7 @@ int vfio_get_region_info(VFIODevice *vbasedev, int index,
>                           struct vfio_region_info **info);
>  int vfio_get_dev_region_info(VFIODevice *vbasedev, uint32_t type,
>                               uint32_t subtype, struct vfio_region_info 
> **info);
> +bool vfio_is_cap_present(VFIODevice *vbasedev, uint16_t cap_type, int 
> region);
>  #endif
>  extern const MemoryListener vfio_prereg_listener;
>  
> diff --git a/linux-headers/linux/vfio.h b/linux-headers/linux/vfio.h
> index 4312e96..b45182e 100644
> --- a/linux-headers/linux/vfio.h
> +++ b/linux-headers/linux/vfio.h
> @@ -301,6 +301,11 @@ struct vfio_region_info_cap_type {
>  #define VFIO_REGION_SUBTYPE_INTEL_IGD_HOST_CFG       (2)
>  #define VFIO_REGION_SUBTYPE_INTEL_IGD_LPC_CFG        (3)
>  
> +/*
> + * The MSIX mappable capability informs that MSIX data of a BAR can be 
> mmapped.
> + */
> +#define VFIO_REGION_INFO_CAP_MSIX_MAPPABLE   3
> +
>  /**
>   * VFIO_DEVICE_GET_IRQ_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 9,
>   *                               struct vfio_irq_info)
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 9de63f0..693394a 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2772,6 +2772,11 @@ 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);
> @@ -2853,6 +2858,8 @@ static void spapr_machine_initfn(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);

I prefer the approach where the property is in the PCI device, set by
the machine defaults mechanism, rather than the property being in the
machine and the device having to look it up.

If Alex prefers the latter though, I'm ok with that way around.

>  }
>  
>  static void spapr_machine_finalizefn(Object *obj)
> @@ -3742,6 +3749,7 @@ static const TypeInfo spapr_machine_info = {
>  /*
>   * pseries-2.11
>   */
> +
>  static void spapr_machine_2_11_instance_options(MachineState *machine)
>  {
>  }
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 1fb8a8e..da5f182 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -1411,6 +1411,21 @@ int vfio_get_dev_region_info(VFIODevice *vbasedev, 
> uint32_t type,
>      return -ENODEV;
>  }
>  
> +bool vfio_is_cap_present(VFIODevice *vbasedev, uint16_t cap_type, int region)
> +{
> +    struct vfio_region_info *info = NULL;
> +    bool ret = false;
> +
> +    if (!vfio_get_region_info(vbasedev, region, &info)) {
> +        if (vfio_get_region_info_cap(info, cap_type)) {
> +            ret = true;
> +        }
> +        g_free(info);
> +    }
> +
> +    return ret;
> +}
> +
>  /*
>   * Interfaces for IBM EEH (Enhanced Error Handling)
>   */
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index c977ee3..27a3706 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -1289,6 +1289,11 @@ static void vfio_pci_fixup_msix_region(VFIOPCIDevice 
> *vdev)
>      off_t start, end;
>      VFIORegion *region = &vdev->bars[vdev->msix->table_bar].region;
>  
> +    if (vfio_is_cap_present(&vdev->vbasedev, 
> VFIO_REGION_INFO_CAP_MSIX_MAPPABLE,
> +                            vdev->msix->table_bar)) {
> +        return;
> +    }
> +
>      /*
>       * We expect to find a single mmap covering the whole BAR, anything else
>       * means it's either unsupported or already setup.
> @@ -1432,6 +1437,15 @@ static void vfio_msix_early_setup(VFIOPCIDevice *vdev, 
> Error **errp)
>      vfio_pci_fixup_msix_region(vdev);
>  }
>  
> +static MemoryRegion *vfio_msix_parent(VFIORegion *region)
> +{
> +    if (region->nr_mmaps == 1 && region->mmaps[0].size == region->size) {
> +        return &region->mmaps[0].mem;
> +    }
> +
> +    return region->mem;
> +}
> +
>  static int vfio_msix_setup(VFIOPCIDevice *vdev, int pos, Error **errp)
>  {
>      int ret;
> @@ -1440,9 +1454,9 @@ static int vfio_msix_setup(VFIOPCIDevice *vdev, int 
> pos, Error **errp)
>      vdev->msix->pending = g_malloc0(BITS_TO_LONGS(vdev->msix->entries) *
>                                      sizeof(unsigned long));
>      ret = msix_init(&vdev->pdev, vdev->msix->entries,
> -                    vdev->bars[vdev->msix->table_bar].region.mem,
> +                    
> vfio_msix_parent(&vdev->bars[vdev->msix->table_bar].region),
>                      vdev->msix->table_bar, vdev->msix->table_offset,
> -                    vdev->bars[vdev->msix->pba_bar].region.mem,
> +                    
> vfio_msix_parent(&vdev->bars[vdev->msix->pba_bar].region),
>                      vdev->msix->pba_bar, vdev->msix->pba_offset, pos,
>                      &err);
>      if (ret < 0) {
> @@ -1473,6 +1487,11 @@ static int vfio_msix_setup(VFIOPCIDevice *vdev, int 
> pos, Error **errp)
>       */
>      memory_region_set_enabled(&vdev->pdev.msix_pba_mmio, false);
>  
> +    if (object_property_get_bool(OBJECT(qdev_get_machine()),
> +                                 "vfio-no-msix-emulation", NULL)) {
> +        memory_region_set_enabled(&vdev->pdev.msix_table_mmio, false);
> +    }
> +

As Alex pointed out elsewhere, the need for the MSI-X emulation isn't
really VFIO specific.  It would make more sense to have the test
directly in msix_init(), and have it skip adding the msix region to
the BAR if the machine has said it's not necessary.

>      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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