Re: [PATCH 1/9] iommu: introduce iova_to_phys_length in iommu_domain_ops

[guanghuifeng@xxxxxxxxxxxxxxxxx]

在 2026/6/1 7:51, Jason Gunthorpe 写道:
> On Sun, May 31, 2026 at 05:36:29PM +0800, Guanghui Feng wrote:
> > Add iova_to_phys_length callback to struct iommu_domain_ops alongside
> > the existing iova_to_phys. The new callback returns both the physical
> > address and the PTE mapping page size in a single page table walk.
> >
> > Add iommu_iova_to_phys_length() core function that:
> > - Checks ops->iova_to_phys_length first (preferred path)
> > - Falls back to ops->iova_to_phys for unmigrated drivers
> >
> > This enables callers like VFIO to efficiently traverse IOVA space
> > by actual mapping granularity instead of fixed PAGE_SIZE steps.
> >
> > Signed-off-by: Guanghui Feng <guanghuifeng@xxxxxxxxxxxxxxxxx>
> > Acked-by: Shiqiang Zhang <shiyu.zsq@xxxxxxxxxxxxxxxxx>
> > Acked-by: Simon Guo <wei.guo.simon@xxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/iommu.c | 34 ++++++++++++++++++++++++++++++++--
> >   include/linux/iommu.h |  9 +++++++++
> >   2 files changed, 41 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index d1a9e713d3a0..43323229a1df 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -2545,15 +2545,45 @@ void iommu_detach_group(struct iommu_domain *domain, struct iommu_group *group)
> >   }
> >   EXPORT_SYMBOL_GPL(iommu_detach_group);
> >   
> > -phys_addr_t iommu_iova_to_phys(struct iommu_domain *domain, dma_addr_t iova)
> > +/**
> > + * iommu_iova_to_phys_length - Translate IOVA and return mapping page size
> > + * @domain: IOMMU domain to query
> > + * @iova: IO virtual address to translate
> > + * @mapped_length: Output parameter for the PTE page size (e.g. 4KB/2MB/1GB)
> > + *
> > + * Like iommu_iova_to_phys() but additionally returns the page size of the
> > + * PTE mapping at @iova through @mapped_length.
> > + *
> > + * Return: The physical address for the given IOVA, or 0 if no translation.
> > + */
> When introducing the new function I would like to fix this 0 error as
> well, it should return PHYS_MAX for error

Implementations such as arm_smmu_iova_to_phys/DOMAIN_NS(iova_to_phys)

all use a return value of 0 as an invalid state, so 0 is used as the 
representation

of an invalid state to maintain compatibility.

> > +phys_addr_t iommu_iova_to_phys_length(struct iommu_domain *domain,
> > +				       dma_addr_t iova,
> > +				       size_t *mapped_length)
> >   {
> > +	if (mapped_length)
> > +		*mapped_length = 0;
> > +
> >   	if (domain->type == IOMMU_DOMAIN_IDENTITY)
> >   		return iova;
> >   
> >   	if (domain->type == IOMMU_DOMAIN_BLOCKED)
> >   		return 0;
> Any domain that doesn't have an op should fail, blocked is one example

In accordance with the implementation of iommu_iova_to_phys, it returns 
a phy value of 0 in invalid states.

> >   
> > -	return domain->ops->iova_to_phys(domain, iova);
> > +	if (domain->ops->iova_to_phys_length)
> > +		return domain->ops->iova_to_phys_length(domain, iova,
> > +							mapped_length);
> > +
> > +	/* Fallback to legacy iova_to_phys without length info */
> > +	if (domain->ops->iova_to_phys)
> > +		return domain->ops->iova_to_phys(domain, iova);
> If it falls back it should return something sensible for the length.
>
> I suggest you approach the patch plan a little differently, the first
> patches should implement the new function and an iommput
> implementation
>
> Arrange things so the normal iova_to_phys calls the new function if it
> is available and discards the length.
>
> Then convert callers that can take advantage of it. Have the fallback
> path also compute the length by iterating internally.
>
> Finally one patch per driver implementing the new op, this could even
> be a second series.
>
> Don't remove iova_to_phys(), it is fine for things that don't need the
> length.

Does this mean retaining the iommu_iova_to_phys implementation but

implementing it through domain->ops->iova_to_phys_length (mapped_length 
is NULL)?

> Jason