Re: [PATCH v4 2/3] gup: introduce unpin_user_folio_dirty_locked()

[David Hildenbrand]

On 18.06.25 08:28, lizhe.67@xxxxxxxxxxxxx wrote:
> On Tue, 17 Jun 2025 12:22:10 -0300, jgg@xxxxxxxx wrote:
>   
> > Weird, but I would not expect this as a general rule, not sure we
> > should rely on it.
> >
> > I would say exported function should not get automatically
> > inlined. That throws all the kprobes into chaos :\
> >
> > BTW, why can't the other patches in this series just use
> > unpin_user_page_range_dirty_lock? The way this stuff is supposed to
> > work is to combine adjacent physical addresses and then invoke
> > unpin_user_page_range_dirty_lock() on the start page of the physical
> > range. This is why we have the gup_folio_range_next() which does the
> > segmentation in an efficient way.
> >
> > Combining adjacent physical is basically free math.
> >
> > Segmenting to folios in the vfio side doesn't make a lot of sense,
> > IMHO.
> >
> >   drivers/vfio/vfio_iommu_type1.c | 35 +++++++++++++++++++++++++++++----
> >   1 file changed, 31 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index e952bf8bdfab..159ba80082a8 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -806,11 +806,38 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, dma_addr_t iova,
> >   				    bool do_accounting)
> >   {
> >   	long unlocked = 0, locked = vpfn_pages(dma, iova, npage);
> > -	long i;
> >   
> > -	for (i = 0; i < npage; i++)
> > -		if (put_pfn(pfn++, dma->prot))
> > -			unlocked++;
> > +	while (npage) {
> > +		long nr_pages = 1;
> > +
> > +		if (!is_invalid_reserved_pfn(pfn)) {
> > +			struct page *page = pfn_to_page(pfn);
> > +			struct folio *folio = page_folio(page);
> > +			long folio_pages_num = folio_nr_pages(folio);
> > +
> > +			/*
> > +			 * For a folio, it represents a physically
> > +			 * contiguous set of bytes, and all of its pages
> > +			 * share the same invalid/reserved state.
> > +			 *
> > +			 * Here, our PFNs are contiguous. Therefore, if we
> > +			 * detect that the current PFN belongs to a large
> > +			 * folio, we can batch the operations for the next
> > +			 * nr_pages PFNs.
> > +			 */
> > +			if (folio_pages_num > 1)
> > +				nr_pages = min_t(long, npage,
> > +					folio_pages_num -
> > +					folio_page_idx(folio, page));
> > +
> > +			unpin_user_folio_dirty_locked(folio, nr_pages,
> > +					dma->prot & IOMMU_WRITE);
>
> Are you suggesting that we should directly call
> unpin_user_page_range_dirty_lock() here (patch 3/3) instead?
>
> BTW, it appears that implementing unpin_user_folio_dirty_locked()
> as an inline function may not be viable for vfio, given that
> gup_put_folio() is not exported.

The compiler seems to properly inline like before, so I think we can 
keep that. @Jason correct me if I am wrong.

--
Cheers,

David / dhildenb