Re: [PATCH v2 1/3] virtio-iommu: Add an option to define the input range width

[Eric Auger]

Hi Jean,

On 2/5/24 11:13, Jean-Philippe Brucker wrote:
> Hi Eric,
>
> On Thu, Feb 01, 2024 at 05:32:22PM +0100, Eric Auger wrote:
>> aw-bits is a new option that allows to set the bit width of
>> the input address range. This value will be used as a default for
>> the device config input_range.end. By default it is set to 64 bits
>> which is the current value.
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>
>> ---
>>
>> v1 -> v2:
>> - Check the aw-bits value is within [32,64]
>> ---
>>  include/hw/virtio/virtio-iommu.h | 1 +
>>  hw/virtio/virtio-iommu.c         | 7 ++++++-
>>  2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/hw/virtio/virtio-iommu.h 
>> b/include/hw/virtio/virtio-iommu.h
>> index 781ebaea8f..5fbe4677c2 100644
>> --- a/include/hw/virtio/virtio-iommu.h
>> +++ b/include/hw/virtio/virtio-iommu.h
>> @@ -66,6 +66,7 @@ struct VirtIOIOMMU {
>>      bool boot_bypass;
>>      Notifier machine_done;
>>      bool granule_frozen;
>> +    uint8_t aw_bits;
>>  };
>>  
>>  #endif
>> diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
>> index ec2ba11d1d..7870bdbeee 100644
>> --- a/hw/virtio/virtio-iommu.c
>> +++ b/hw/virtio/virtio-iommu.c
>> @@ -1314,7 +1314,11 @@ static void virtio_iommu_device_realize(DeviceState 
>> *dev, Error **errp)
>>       */
>>      s->config.bypass = s->boot_bypass;
>>      s->config.page_size_mask = qemu_real_host_page_mask();
>> -    s->config.input_range.end = UINT64_MAX;
>> +    if (s->aw_bits < 32 || s->aw_bits > 64) {
> I'm wondering if we should lower this to 16 bits, just to support all
> possible host SMMU configurations (the smallest address space configurable
> with T0SZ is 25-bit, or 16-bit with the STT extension).
I have no objection relaxing that check. Alex suggested this 32b low
limit with his knowledge of x86. I am a bit reluctant to add extra
machine specific checks though. Anyway I assume that some [low] aw-bits
will fail with some guests and this will be difficult to understand from
bug reports.

Thanks

Eric
>
> Thanks,
> Jean
>
>> +        error_setg(errp, "aw-bits must be within [32,64]");
>> +    }
>> +    s->config.input_range.end =
>> +        s->aw_bits == 64 ? UINT64_MAX : BIT_ULL(s->aw_bits) - 1;
>>      s->config.domain_range.end = UINT32_MAX;
>>      s->config.probe_size = VIOMMU_PROBE_SIZE;
>>  
>> @@ -1525,6 +1529,7 @@ static Property virtio_iommu_properties[] = {
>>      DEFINE_PROP_LINK("primary-bus", VirtIOIOMMU, primary_bus,
>>                       TYPE_PCI_BUS, PCIBus *),
>>      DEFINE_PROP_BOOL("boot-bypass", VirtIOIOMMU, boot_bypass, true),
>> +    DEFINE_PROP_UINT8("aw-bits", VirtIOIOMMU, aw_bits, 64),
>>      DEFINE_PROP_END_OF_LIST(),
>>  };
>>  
>> -- 
>> 2.41.0
>>