linux-kernel - RE: [PATCH] xen/swiotlb: correct the check for xen_destroy_contiguous

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Date:   Tue, 28 Apr 2020 08:21:57 +0000
From:   Peng Fan <peng.fan@....com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
        "jgross@...e.com" <jgross@...e.com>,
        "sstabellini@...nel.org" <sstabellini@...nel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] xen/swiotlb: correct the check for
 xen_destroy_contiguous_region

> Subject: Re: [PATCH] xen/swiotlb: correct the check for
> xen_destroy_contiguous_region
> 
> On Tue, Apr 28, 2020 at 03:33:45PM +0800, peng.fan@....com wrote:
> >
> > In xen_swiotlb_alloc_coherent, if !(dev_addr + size - 1 <= dma_mask)
> > or range_straddles_page_boundary(phys, size) are true, it will create
> > contiguous region. So when free, we need to free contiguous region use
> > upper check condition.
> >
> > Signed-off-by: Peng Fan <peng.fan@....com>
> > ---
> >  drivers/xen/swiotlb-xen.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> > index b6d27762c6f8..ab96e468584f 100644
> > --- a/drivers/xen/swiotlb-xen.c
> > +++ b/drivers/xen/swiotlb-xen.c
> > @@ -346,8 +346,8 @@ xen_swiotlb_free_coherent(struct device *hwdev,
> size_t size, void *vaddr,
> >  	/* Convert the size to actually allocated. */
> >  	size = 1UL << (order + XEN_PAGE_SHIFT);
> >
> > -	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
> > -		     range_straddles_page_boundary(phys, size)) &&
> > +	if (((dev_addr + size - 1 > dma_mask) ||
> > +	    range_straddles_page_boundary(phys, size)) &&
> >  	    TestClearPageXenRemapped(virt_to_page(vaddr)))
> 
> No need for the inner braces.
> 
> But more importantly please factor our a helper that can be used by alloc and
> free to make sure that they always stay in sync.  Something

Thanks for reviewing. I'll take your suggestion in v2. Before that,
I would wait to see if there are more comments in this patch,
because there are several history commits touching this place.

Thanks,
Peng.

> like:
> 
> static inline bool xen_swiotlb_need_contiguous_region(struct device *dev,
> 		phys_addr_t phys, size_t size)
> {
> 
> 	return xen_phys_to_bus(phys) + size - 1 > dev->coherent_dma_mask ||
> 		range_straddles_page_boundary(phys, size)) }