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

["Cédric Le Goater" <clg@redhat.com>]

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"

Not that much. The IOMMU_IOAS_MAP failure becomes a "Bad address".

Thanks,

C.