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

[Alex Williamson]

On Wed, 24 Jan 2024 14:14:19 +0100
Eric Auger <eric.auger@redhat.com> wrote:

> Hi Alex,
> 
> On 1/24/24 00:51, Alex Williamson wrote:
> > On Tue, 23 Jan 2024 19:15:55 +0100
> > Eric Auger <eric.auger@redhat.com> 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>
> >> ---
> >>  include/hw/virtio/virtio-iommu.h | 1 +
> >>  hw/virtio/virtio-iommu.c         | 4 +++-
> >>  2 files changed, 4 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..e7f299e0c6 100644
> >> --- a/hw/virtio/virtio-iommu.c
> >> +++ b/hw/virtio/virtio-iommu.c
> >> @@ -1314,7 +1314,8 @@ 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;
> >> +    s->config.input_range.end =
> >> +        s->aw_bits == 64 ? UINT64_MAX : BIT_ULL(s->aw_bits) - 1;  
> > What happens when someone sets aw_bits = 1?  There are a whole bunch of
> > impractical values here ripe for annoying bug reports.  vtd_realize()
> > returns an Error for any values other than 39 or 48.  We might pick an
> > arbitrary lower bound (39?) or some other more creative solution here
> > to avoid those silly issues in our future.  Thanks,  
> You're right. I can check the input value. This needs to be dependent on
> the machine though but this should be feasable.
> Then I would allow 39 and 48 for q35 and 64 only on ARM.

AFAIK AMD-Vi supports 64-bit address space.  Without querying the host
there's no way to place an accurate limit below 64-bit.  Thanks,

Alex

> >>      s->config.domain_range.end = UINT32_MAX;
> >>      s->config.probe_size = VIOMMU_PROBE_SIZE;
> >>  
> >> @@ -1525,6 +1526,7 @@ 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(),
> >>  };
> >>    
>