Re: [PATCH] vfio: add dma map/unmap support for noiommu

[William Tu <witu@nvidia.com>]

On 5/5/25 10:16 AM, Jason Gunthorpe wrote:
> On Fri, May 02, 2025 at 05:48:21PM -0700, William Tu wrote:
>> Currently when using noiommu, the VFIO uAPI does not support
>> VFIO_IOMMU_MAP_DMA, causing userspace VFIO program to use
>> s.t like /proc/self/pagemap to get the physical address.
>> The patch adds the support for dma map and unmap operation
>> for noiommu.
> We are not changing vfio container code in significant ways now, new
> features need to go through iommufd and use an access to do this.
>
>> +	while (remaining_pages > 0) {
>> +		unsigned long pages_to_unmap = min(remaining_pages, chunk_size);
>> +
>> +		ret = get_user_pages_remote(mm, current_vaddr, pages_to_unmap,
>> +					    FOLL_GET, pages, NULL);
>> +		if (ret > 0) {
> This doesn't work anyhow because there is no guarentee that the 2nd
> get_user_pages will return the same things, and that is the wrong API
> to use anyhow.
>
> Jason
Hi Jason,
Thanks for the feedback. Will drop this one and use the correct API.
William