Re: [PATCH v3 3/5] fix vmap_udmabuf error page set

[Huan Yang]

在 2024/8/17 8:54, Kasireddy, Vivek 写道:
> Hi Huan,
>
> > Subject: [PATCH v3 3/5] fix vmap_udmabuf error page set
> Please prepend a "udmabuf:" to the subject line and improve the wording.
OK, sorry for this mistake.
> > Currently vmap_udmabuf set page's array by each folio.
> > But, ubuf->folios is only contain's the folio's head page.
> >
> > That mean we repeatedly mapped the folio head page to the vmalloc area.
> >
> > Due to udmabuf can use hugetlb, if HVO enabled, tail page may not exist,
> > so, we can't use page array to map, instead, use pfn array.
> >
> > Signed-off-by: Huan Yang <link@xxxxxxxx>
> > Suggested-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
> > ---
> >   drivers/dma-buf/udmabuf.c | 22 +++++++++++++++-------
> >   1 file changed, 15 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> > index 3ec72d47bb1c..4ec54c60d76c 100644
> > --- a/drivers/dma-buf/udmabuf.c
> > +++ b/drivers/dma-buf/udmabuf.c
> > @@ -67,21 +67,29 @@ static int mmap_udmabuf(struct dma_buf *buf,
> > struct vm_area_struct *vma)
> >   static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
> >   {
> >   	struct udmabuf *ubuf = buf->priv;
> > -	struct page **pages;
> > +	unsigned long *pfns;
> I wish there was a way to easily test the vmap scenario but its great that

It need a driver set in kernel. maybe write a debug code in udmabuf?(not 
sure)

> you are able to eliminate the usage of "struct page" completely from
> udmabuf driver, with this patch.
>
> >   	void *vaddr;
> >   	pgoff_t pg;
> >
> >   	dma_resv_assert_held(buf->resv);
> >
> > -	pages = kvmalloc_array(ubuf->pagecount, sizeof(*pages),
> > GFP_KERNEL);
> > -	if (!pages)
> > +	/**
> > +	 * HVO may free tail pages, so just use pfn to map each folio
> > +	 * into vmalloc area.
> > +	 */
> > +	pfns = kvmalloc_array(ubuf->pagecount, sizeof(*pfns), GFP_KERNEL);
> > +	if (!pfns)
> >   		return -ENOMEM;
> >
> > -	for (pg = 0; pg < ubuf->pagecount; pg++)
> > -		pages[pg] = &ubuf->folios[pg]->page;
> > +	for (pg = 0; pg < ubuf->pagecount; pg++) {
> > +		unsigned long pfn = folio_pfn(ubuf->folios[pg]);
> >
> > -	vaddr = vm_map_ram(pages, ubuf->pagecount, -1);
> > -	kvfree(pages);
> > +		pfn += ubuf->offsets[pg] >> PAGE_SHIFT;
> > +		pfns[pg] = pfn;
> > +	}
> > +
> > +	vaddr = vmap_pfn(pfns, ubuf->pagecount, PAGE_KERNEL);
> Looks like this would require a "select VMAP_PFN" in Kconfig.

Yes, I miss this.

Thank you too much.

> Thanks,
> Vivek
>
> > +	kvfree(pfns);
> >   	if (!vaddr)
> >   		return -EINVAL;
> >
> > --
> > 2.45.2