Re: [PATCH v6 01/21] backends/iommufd: Introduce the iommufd object

[Cédric Le Goater]

On 11/17/23 14:29, Eric Auger wrote:
> Hi Cédric,
>
> On 11/17/23 12:39, Duan, Zhenzhong wrote:
> > Hi Cédric,
> >
> > > -----Original Message-----
> > > From: Cédric Le Goater <clg@redhat.com>
> > > Sent: Friday, November 17, 2023 7:10 PM
> > > Subject: Re: [PATCH v6 01/21] backends/iommufd: Introduce the iommufd object
> > >
> > > Hello,
> > >
> > > > +int iommufd_backend_map_dma(IOMMUFDBackend *be, uint32_t ioas_id,
> > > hwaddr iova,
> > > > +                            ram_addr_t size, void *vaddr, bool readonly)
> > > > +{
> > > > +    int ret, fd = be->fd;
> > > > +    struct iommu_ioas_map map = {
> > > > +        .size = sizeof(map),
> > > > +        .flags = IOMMU_IOAS_MAP_READABLE |
> > > > +                 IOMMU_IOAS_MAP_FIXED_IOVA,
> > > > +        .ioas_id = ioas_id,
> > > > +        .__reserved = 0,
> > > > +        .user_va = (uintptr_t)vaddr,
> > > > +        .iova = iova,
> > > > +        .length = size,
> > > > +    };
> > > > +
> > > > +    if (!readonly) {
> > > > +        map.flags |= IOMMU_IOAS_MAP_WRITEABLE;
> > > > +    }
> > > > +
> > > > +    ret = ioctl(fd, IOMMU_IOAS_MAP, &map);
> > > > +    trace_iommufd_backend_map_dma(fd, ioas_id, iova, size,
> > > > +                                  vaddr, readonly, ret);
> > > > +    if (ret) {
> > > > +        ret = -errno;
> > > > +        error_report("IOMMU_IOAS_MAP failed: %m");
> > > > +    }
> > > > +    return ret;
> > > > +}
> > > When using a UEFI guest, QEMU reports errors when mapping regions
> > > in the top PCI space :
> > >
> > >    iommufd_backend_map_dma  iommufd=10 ioas=2 iova=0x380000001000
> > > size=0x3000 addr=0x7fce2c28b000 readonly=0 (-1)
> > >    qemu-system-x86_64: IOMMU_IOAS_MAP failed: Invalid argument
> > >    qemu-system-x86_64: vfio_container_dma_map(0x55a21b03a150,
> > > 0x380000001000, 0x3000, 0x7fce2c28b000) = -22 (Invalid argument)
> > >
> > >    iommufd_backend_map_dma  iommufd=10 ioas=2 iova=0x380000004000
> > > size=0x4000 addr=0x7fce2c980000 readonly=0 (-1)
> > >    qemu-system-x86_64: IOMMU_IOAS_MAP failed: Invalid argument
> > >    qemu-system-x86_64: vfio_container_dma_map(0x55a21b03a150,
> > > 0x380000004000, 0x4000, 0x7fce2c980000) = -22 (Invalid argument)
> > >
> > > This is because IOMMUFD reserved IOVAs areas are :
> > >
> > >   [ fee00000 - feefffff ]
> > >   [ 8000000000 - ffffffffffffffff ] (39 bits address space)
> > >
> > > which were allocated when the device was initially attached.
> > > The topology is basic. Something is wrong.
> >         
> > Thanks for your report. This looks a hardware limit of
> > host IOMMU address width(39) < guest physical address width.
> >
> > A similar issue with a fix submitted below, ccing related people.
> > https://lists.gnu.org/archive/html/qemu-devel/2023-11/msg02937.html
> > It looks the fix will not work for hotplug.
> >
> > Or below qemu cmdline may help:
> > "-cpu host,host-phys-bits-limit=39"
>
> don't you have the same issue with legacy VFIO code, you should?

I tend to be lazy and use seabios for guests on the command line.
I do see the error with legacy VFIO and uefi.

However, with the address space size work-around and iommufd, the
error is different, an EFAULT now. Some page pinning issue it seems.

Thanks,

C.