Re: [RFC V1 02/12] iommufd: no DMA to BARs

[Steven Sistare <steven.sistare@oracle.com>]

On 8/12/2024 9:39 PM, Yi Liu wrote:
> On 2024/7/21 03:15, Steve Sistare wrote:
>> Do not map VFIO PCI BARs for DMA.  This stops a raft of warnings of the
>> following form at QEMU start time when using -object iommufd:
>>
>> qemu-kvm: warning: IOMMU_IOAS_MAP failed: Bad address, PCI BAR?
>> qemu-kvm: vfio_container_dma_map(0x555558282db0, 0x8800010000, 0x4000, 0x7ffff7ff0000) = -14 (Bad address)
> 
> It is required as Alex pointed, so no need to pay further attempt to hide
> this message. And there were efforts to make it. But not done yet. Below
> links may be helpful if you are interested about the history.
> 
> [1] https://lore.kernel.org/kvm/14-v4-0de2f6c78ed0+9d1-iommufd_jgg@nvidia.com/
> [2] https://lore.kernel.org/kvm/20240624141139.GH29266@unreal/
> [3] https://lore.kernel.org/kvm/0-v1-9e6e1739ed95+5fa-vfio_dma_buf_jgg@nvidia.com/

Thanks for the pointers.  Good to here the problem is being worked.

- Steve

>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>   hw/vfio/common.c      | 3 ++-
>>   hw/vfio/helpers.c     | 1 +
>>   include/exec/memory.h | 1 +
>>   3 files changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index da2e0ec..403d45a 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -248,7 +248,8 @@ static bool vfio_listener_skipped_section(MemoryRegionSection *section)
>>               * are never accessed by the CPU and beyond the address width of
>>               * some IOMMU hardware.  TODO: VFIO should tell us the IOMMU width.
>>               */
>> -           section->offset_within_address_space & (1ULL << 63);
>> +           section->offset_within_address_space & (1ULL << 63) ||
>> +           section->mr->no_dma;
>>   }
>>   /* Called with rcu_read_lock held.  */
>> diff --git a/hw/vfio/helpers.c b/hw/vfio/helpers.c
>> index b14edd4..e4cfdd2 100644
>> --- a/hw/vfio/helpers.c
>> +++ b/hw/vfio/helpers.c
>> @@ -435,6 +435,7 @@ int vfio_region_mmap(VFIORegion *region)
>>                                             memory_region_owner(region->mem),
>>                                             name, region->mmaps[i].size,
>>                                             region->mmaps[i].mmap);
>> +        region->mmaps[i].mem.no_dma = true;
>>           g_free(name);
>>           memory_region_add_subregion(region->mem, region->mmaps[i].offset,
>>                                       &region->mmaps[i].mem);
>> diff --git a/include/exec/memory.h b/include/exec/memory.h
>> index ea03ef2..850cc8c 100644
>> --- a/include/exec/memory.h
>> +++ b/include/exec/memory.h
>> @@ -794,6 +794,7 @@ struct MemoryRegion {
>>       bool unmergeable;
>>       uint8_t dirty_log_mask;
>>       bool is_iommu;
>> +    bool no_dma;
>>       RAMBlock *ram_block;
>>       Object *owner;
>>       /* owner as TYPE_DEVICE. Used for re-entrancy checks in MR access hotpath */
>