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

["Cédric Le Goater" <clg@redhat.com>]

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.