Re: [Qemu-ppc] [RFC PATCH qemu v6] vfio-pci: Allow mmap of MSIX BAR

[Alexey Kardashevskiy]

On 01/02/18 05:57, Alex Williamson wrote:
> On Wed, 31 Jan 2018 18:24:45 +1100
> Alexey Kardashevskiy <address@hidden> 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".
>>
>> This change may affect machines which are using MSIX emulation and
>> mapping MMIO RAM regions for DMA as previously MSIX containing BAR
>> would be split in chunks aligned to the system page size and we would
>> only see aligned RAM memory sections in vfio_listener_region_add/del.
>> As the system page size is usually is equal or bigger than the IOMMU
>> page size, vfio_dma_map() did not have a legitimate reason to fail so
>> mapping failures were fatal. Note that this behaviour silently skips
>> parts of BARs adjacent to the MSIX data.
>>
>> With this change, we map entire MSIX BAR and emulate MSIX on top of it
>> so vfio_listener_region_add/del may be called with unaligned MMIO RAM
>> regions and vfio_dma_map() will fail&exit on these. In order to mitigate
>> this, this changes vfio_listener_region_add() not to try vfio_dma_map() if
>> the memory section is not aligned to the minimal IOMMU page; an error
>> is printed instead. This also treats all errors from vfio_dma_map()
>> non fatal when the listener is called on the MMIO RAM region.
>> vfio_listener_region_del() is adjusted accordingly.
>>
>> If the amount of errors printed is overwhelming, the MSIX relocation
>> could be used to avoid excessive error output.
>>
>> This requires the kernel change - "vfio-pci: Allow mapping MSIX BAR" -
>> for the new capability: https://www.spinics.net/lists/kvm/msg160282.html
> 
> Looks like there are at least 3 or 4 patches here:

RFC...


> A) Update linux-headers (gated by v4.16-rc1)

Sure, I just do not see it in any upstream yet.


> B) vfio_is_cap_present
> C) check alignment on region_add/del vs hostwin, non-fatal ram_device


Having B) without C) will break bisectability. Having C) before B) will not
trigger any new code paths so it will break bisectability too. I'd have B)
and C) in a single patch.

> D) platform directed disabling of MSI-X MemoryRegion

Sure.


>  
>> Signed-off-by: Alexey Kardashevskiy <address@hidden>
>> ---
>> Changes:
>> v6:
>> * dropped that stupid p2p property patch
>>
>> v5:
>> * rebased on top of 'p2p' proposed patch
>>
>> 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              | 66 
>> +++++++++++++++++++++++++++++++++++++++----
>>  hw/vfio/pci.c                 | 10 +++++++
>>  5 files changed, 83 insertions(+), 6 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 32a876b..6d333e2 100644
>> --- a/hw/ppc/spapr.c
>> +++ b/hw/ppc/spapr.c
>> @@ -2830,6 +2830,11 @@ 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);
>> @@ -2911,6 +2916,8 @@ 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..9100a42 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -508,6 +508,18 @@ static void vfio_listener_region_add(MemoryListener 
>> *listener,
>>      }
>>  
>>      /* Here we assume that memory_region_is_ram(section->mr)==true */
>> +    if (memory_region_is_ram_device(section->mr)) {
>> +        hwaddr pgmask = (1ULL << ctz64(hostwin->iova_pgsizes)) - 1;
>> +
>> +        if ((section->offset_within_region & pgmask) ||
>> +            (int128_getlo(section->size) & pgmask)) {
> 
> Why are we working on section->foo variables when the vfio_dma_map()
> we're trying to avoid is based on the calculated iova and llsize?

Ah, mostly because I was thinking of vaddr (which is incorrect).

But still iova and llsize are target page size aligned, and IOMMU may have
a smaller page size and I wanted to protect against that. btw should not
vfio_listener_region_add() use IOMMU page size rather than
TARGET_PAGE_MASK? The VFIOHostDMAWindow was not there at the time but now
it is.



> 
>> +            error_report("Region %"HWADDR_PRIx"..%"HWADDR_PRIx" is not 
>> aligned to %"HWADDR_PRIx" and cannot be mapped for DMA",
> 
> There's plenty of opportunity to wrap this at a variable.
> 
>> +                         section->offset_within_region,
>> +                         int128_getlo(section->size),
>> +                         pgmask + 1);
>> +            return;
>> +        }
>> +    }
>>  
>>      vaddr = memory_region_get_ram_ptr(section->mr) +
>>              section->offset_within_region +
>> @@ -523,6 +535,9 @@ static void vfio_listener_region_add(MemoryListener 
>> *listener,
>>          error_report("vfio_dma_map(%p, 0x%"HWADDR_PRIx", "
>>                       "0x%"HWADDR_PRIx", %p) = %d (%m)",
>>                       container, iova, int128_get64(llsize), vaddr, ret);
>> +        if (memory_region_is_ram_device(section->mr)) {
>> +            return;
>> +        }
> 
> So this one is mostly paranoia that it's an MMIO mapping that we think
> should have worked, but didn't?


Paranoia or/and ignorance. I do not really know why else it might fail,
what if the IOMMU is known not to support MMIO and such mapping will fail?


> 
>>          goto fail;
>>      }
>>  
>> @@ -550,6 +565,7 @@ static void vfio_listener_region_del(MemoryListener 
>> *listener,
>>      hwaddr iova, end;
>>      Int128 llend, llsize;
>>      int ret;
>> +    bool try_unmap = true;
>>  
>>      if (vfio_listener_skipped_section(section)) {
>>          trace_vfio_listener_region_del_skip(
>> @@ -602,13 +618,36 @@ static void vfio_listener_region_del(MemoryListener 
>> *listener,
>>  
>>      trace_vfio_listener_region_del(iova, end);
>>  
>> -    ret = vfio_dma_unmap(container, iova, int128_get64(llsize));
>> +    if (memory_region_is_ram_device(section->mr)) {
>> +        hwaddr pgmask;
>> +        VFIOHostDMAWindow *hostwin;
>> +        bool hostwin_found;
>> +
>> +        hostwin_found = false;
>> +        QLIST_FOREACH(hostwin, &container->hostwin_list, hostwin_next) {
>> +            if (hostwin->min_iova <= iova && end <= hostwin->max_iova) {
>> +                hostwin_found = true;
>> +                break;
>> +            }
>> +        }
>> +        assert(hostwin_found);
> 
> And we justify this assert because the region_add path would have
> triggered a fatal mapping fault for this condition and therefore
> getting here would mean the region_del doesn't match a previous
> region_add, right?

Yes.


>> +
>> +        pgmask = (1ULL << ctz64(hostwin->iova_pgsizes)) - 1;
>> +
>> +        try_unmap = !(section->offset_within_region & pgmask) &&
>> +            !(int128_getlo(section->size) & pgmask);
> 
> Same question as above with iova & llend.
> 
>> +    }
>> +
>> +    if (try_unmap) {
>> +        ret = vfio_dma_unmap(container, iova, int128_get64(llsize));
>> +        if (ret) {
>> +            error_report("vfio_dma_unmap(%p, 0x%"HWADDR_PRIx", "
>> +                         "0x%"HWADDR_PRIx") = %d (%m)",
>> +                         container, iova, int128_get64(llsize), ret);
>> +        }
>> +    }
>> +
>>      memory_region_unref(section->mr);
>> -    if (ret) {
>> -        error_report("vfio_dma_unmap(%p, 0x%"HWADDR_PRIx", "
>> -                     "0x%"HWADDR_PRIx") = %d (%m)",
>> -                     container, iova, int128_get64(llsize), ret);
>> -    }
>>  
>>      if (container->iommu_type == VFIO_SPAPR_TCE_v2_IOMMU) {
>>          vfio_spapr_remove_window(container,
>> @@ -1386,6 +1425,21 @@ 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)
> 
> How about vfio_has_region_cap() and reorder the params to match,
> vbasedev, region, cap_type.

Sure.


>> +{
>> +    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 2c71295..e23f5cf 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)) {
> 
> It's convenient that BAR# == Region#, but I think the correct reference
> is: vdev->bars[vdev->msix->table_bar].region.nr
> 
> A comment to explain this region fixup exit would be nice.
> 
>> +        return;
>> +    }
>> +
>>      /*
>>       * We expect to find a single mmap covering the whole BAR, anything else
>>       * means it's either unsupported or already setup.
>> @@ -1473,6 +1478,11 @@ static int vfio_msix_setup(VFIOPCIDevice *vdev, int 
>> pos, Error **errp)
>>       */
>>      memory_region_set_enabled(&vdev->pdev.msix_pba_mmio, false);
> 
> A comment here would be nice.
>   
>> +    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;
>>  }
>>  

Thanks for the review!


-- 
Alexey