Re: [Qemu-devel] [PATCH qemu v4] RFC: vfio-pci: Allow mmap of MSIX BAR

[Auger Eric <eric.auger@redhat.com>]

Hi,

On 25/01/18 14:56, Auger Eric wrote:
> Hi Alexey,
> 
> On 25/01/18 05:22, 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 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 may create MMIO RAM memory sections with
>> an address or/and a size not aligned which will make vfio_dma_map() fail;
>> to address this, this treats such failures as non-fatal and does not print
>> an error. This adds a return value from vfio_dma_map() to the tracepoint
>> and moves the latter further down to let the user have a clue why P2P
>> might not work.
>>
>> 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 <aik@ozlabs.ru>
>> ---
>> Changes:
>> v4:
>> * silenced dma map errors if unaligned mapping is attempted - they are going
>> to fail anyway
>>
>> v3:
>> * vfio_listener_region_add() won't make qemu exit if failed on MMIO MR
>> ---
>>  include/hw/vfio/vfio-common.h |  1 +
>>  linux-headers/linux/vfio.h    |  5 +++++
>>  hw/ppc/spapr.c                |  7 +++++++
>>  hw/vfio/common.c              | 27 +++++++++++++++++++++++++--
>>  hw/vfio/pci.c                 | 10 ++++++++++
>>  hw/vfio/trace-events          |  2 +-
>>  6 files changed, 49 insertions(+), 3 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 d1acfe8..5ff43ce 100644
>> --- a/hw/ppc/spapr.c
>> +++ b/hw/ppc/spapr.c
>> @@ -2789,6 +2789,11 @@ 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);
>> @@ -2870,6 +2875,8 @@ 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/common.c b/hw/vfio/common.c
>> index 3d652c8..04a8280 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -513,13 +513,21 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>              section->offset_within_region +
>>              (iova - section->offset_within_address_space);
>>  
>> -    trace_vfio_listener_region_add_ram(iova, end, vaddr);
>> -
>>      llsize = int128_sub(llend, int128_make64(iova));
>>  
>>      ret = vfio_dma_map(container, iova, int128_get64(llsize),
>>                         vaddr, section->readonly);
>> +    trace_vfio_listener_region_add_ram(iova, end, vaddr, ret);
>> +
>>      if (ret) {
>> +        hwaddr pgmask = (1ULL << ctz64(hostwin->iova_pgsizes)) - 1;
>> +
>> +        if (memory_region_is_ram_device(section->mr) &&
>> +            ((section->offset_within_region & pgmask) ||
>> +             (int128_getlo(section->size) & pgmask))) {
>> +            return;
>> +        }
>> +
> Why not avoiding to call vfio_dma_map in this case and print a helpful
> message for the end-user?
> 
> qemu-system-aarch64: VFIO_UNMAP_DMA: -22
> qemu-system-aarch64: vfio_dma_unmap(0xc0dab90, 0x8000000000, 0x2000) =
> -22 (Invalid argument)

By the way there is also the unmap path in vfio_listener_region_del ;-)

Thanks

Eric
> 
> is not self-explanatory I think.
> 
> Thanks
> 
> Eric
>>          error_report("vfio_dma_map(%p, 0x%"HWADDR_PRIx", "
>>                       "0x%"HWADDR_PRIx", %p) = %d (%m)",
>>                       container, iova, int128_get64(llsize), vaddr, ret);
>> @@ -1386,6 +1394,21 @@ 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 359a8f1..a96ece6 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.
>> @@ -1569,6 +1574,11 @@ 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);
>> +    }
>> +
>>      return 0;
>>  }
>>  
>> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
>> index 437ccdd..d747c11 100644
>> --- a/hw/vfio/trace-events
>> +++ b/hw/vfio/trace-events
>> @@ -89,7 +89,7 @@ vfio_region_read(char *name, int index, uint64_t addr, unsigned size, uint64_t d
>>  vfio_iommu_map_notify(const char *op, uint64_t iova_start, uint64_t iova_end) "iommu %s @ 0x%"PRIx64" - 0x%"PRIx64
>>  vfio_listener_region_add_skip(uint64_t start, uint64_t end) "SKIPPING region_add 0x%"PRIx64" - 0x%"PRIx64
>>  vfio_listener_region_add_iommu(uint64_t start, uint64_t end) "region_add [iommu] 0x%"PRIx64" - 0x%"PRIx64
>> -vfio_listener_region_add_ram(uint64_t iova_start, uint64_t iova_end, void *vaddr) "region_add [ram] 0x%"PRIx64" - 0x%"PRIx64" [%p]"
>> +vfio_listener_region_add_ram(uint64_t iova_start, uint64_t iova_end, void *vaddr, int ret) "region_add [ram] 0x%"PRIx64" - 0x%"PRIx64" [%p] ret=%d"
>>  vfio_listener_region_del_skip(uint64_t start, uint64_t end) "SKIPPING region_del 0x%"PRIx64" - 0x%"PRIx64
>>  vfio_listener_region_del(uint64_t start, uint64_t end) "region_del 0x%"PRIx64" - 0x%"PRIx64
>>  vfio_disconnect_container(int fd) "close container->fd=%d"
>>