Re: [PATCH v5 5/9] iommufd: Add an ioctl to query PA from IOVA for noiommu mode

[Jacob Pan]

Hi Jason,

On Wed, 13 May 2026 09:22:21 -0300
Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:

> On Wed, May 13, 2026 at 03:53:43PM +0800, Baolu Lu wrote:
> > >   #define IOMMU_IOAS_MAP _IO(IOMMUFD_TYPE, IOMMUFD_CMD_IOAS_MAP)
> > > +/**
> > > + * struct iommu_ioas_noiommu_get_pa -
> > > ioctl(IOMMU_IOAS_NOIOMMU_GET_PA)
> > > + * @size: sizeof(struct iommu_ioas_noiommu_get_pa)
> > > + * @flags: Reserved, must be 0 for now
> > > + * @ioas_id: IOAS ID to query IOVA to PA mapping from
> > > + * @__reserved: Must be 0
> > > + * @iova: IOVA to query
> > > + * @out_length: Number of bytes contiguous physical address
> > > starting from phys  
> > 
> > Nit: Instead of making this behavior mandatory, would it be
> > valuable to allocate a bit in @flags to toggle this behavior? For
> > extremely large mappings (e.g., several GBs of contiguous
> > hugepages), the loop to determine the contiguous physical addresses
> > might take a long time. A very long scan could theoretically delay
> > userspace DMA setup.  
> 
> If we are worrying about that then a iova/length pair would be
> appropriate such that out_len doesn't exceed the length. Right now it
> stops at the area boundary IIRC.
> 

 Yes, it stops at area boundary. How about renaming out_length to
 length, then use it as both input (cap on the scan range) and output
 (actual contiguous bytes found)? When length == 0 on input, it could
 mean "no limit" to keep the current behavior as default.