Re: [PATCH v3 0/3] VIRTIO-IOMMU: Introduce an aw-bits option

[Eric Auger]

Hi Jean,

On 2/8/24 15:42, Jean-Philippe Brucker wrote:
> On Thu, Feb 08, 2024 at 11:10:16AM +0100, Eric Auger wrote:
>> In [1] and [2] we attempted to fix a case where a VFIO-PCI device
>> protected with a virtio-iommu is assigned to an x86 guest. On x86
>> the physical IOMMU may have an address width (gaw) of 39 or 48 bits
>> whereas the virtio-iommu exposes a 64b input address space by default.
>> Hence the guest may try to use the full 64b space and DMA MAP
>> failures may be encountered. To work around this issue we endeavoured
>> to pass usable host IOVA regions (excluding the out of range space) from
>> VFIO to the virtio-iommu device so that the virtio-iommu driver can
>> query those latter during the probe request and let the guest iommu
>> kernel subsystem carve them out. 
>>
>> However if there are several devices in the same iommu group,
>> only the reserved regions of the first one are taken into
>> account by the iommu subsystem of the guest. This generally
>> works on baremetal because devices are not going to
>> expose different reserved regions. However in our case, this
>> may prevent from taking into account the host iommu geometry.
>>
>> So the simplest solution to this problem looks to introduce an
>> input address width option, aw-bits, which matches what is
>> done on the intel-iommu. By default, from now on it is set
>> to 39 bits with pc_q35 and 48 with arm virt. This replaces the
>> previous default value of 64b. So we need to introduce a compat
>> for machines older than 9.0 to behave similarly. We use
>> hw_compat_8_2 to acheive that goal.
> For the series:
>
> Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

Thanks!

and after reading your v2 last reply we case we need to support smaller
aw ranges, I will do the change when the use case arises.

Eric
>
>> Outstanding series [2] remains useful to let resv regions beeing
>> communicated on time before the probe request.
>>
>> [1] [PATCH v4 00/12] VIRTIO-IOMMU/VFIO: Don't assume 64b IOVA space
>>     
>> https://lore.kernel.org/all/20231019134651.842175-1-eric.auger@redhat.com/
>>     - This is merged -
>>
>> [2] [RFC 0/7] VIRTIO-IOMMU/VFIO: Fix host iommu geometry handling for 
>> hotplugged devices
>>     
>> https://lore.kernel.org/all/20240117080414.316890-1-eric.auger@redhat.com/
>>     - This is pending for review on the ML -
>>
>> This series can be found at:
>> https://github.com/eauger/qemu/tree/virtio-iommu-aw-bits-v3
>> previous
>> https://github.com/eauger/qemu/tree/virtio-iommu-aw-bits-v2
>>
>> Applied on top of [3]
>> [PATCH v2] virtio-iommu: Use qemu_real_host_page_mask as default 
>> page_size_mask
>> https://lore.kernel.org/all/20240117132039.332273-1-eric.auger@redhat.com/
>>
>> History:
>> v2 -> v3:
>> - Collected Zhenzhong and Cédric's R-b + Yanghang's T-b
>> - use &error_abort instead of NULL error handle
>>   on object_property_get_uint() call (Cédric)
>> - use VTD_HOST_AW_39BIT (Cédric)
>>
>> v1 -> v2
>> - Limit aw to 48b on ARM
>> - Check aw is within [32,64]
>> - Use hw_compat_8_2
>>
>>
>> Eric Auger (3):
>>   virtio-iommu: Add an option to define the input range width
>>   virtio-iommu: Trace domain range limits as unsigned int
>>   hw: Set virtio-iommu aw-bits default value on pc_q35 and arm virt
>>
>>  include/hw/virtio/virtio-iommu.h | 1 +
>>  hw/arm/virt.c                    | 6 ++++++
>>  hw/core/machine.c                | 5 ++++-
>>  hw/i386/pc.c                     | 6 ++++++
>>  hw/virtio/virtio-iommu.c         | 7 ++++++-
>>  hw/virtio/trace-events           | 2 +-
>>  6 files changed, 24 insertions(+), 3 deletions(-)
>>
>> -- 
>> 2.41.0
>>