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Date: Thu, 21 May 2020 13:08:56 -0700 (PDT) From: Stefano Stabellini <sstabellini@...nel.org> To: Julien Grall <julien@....org> cc: Stefano Stabellini <sstabellini@...nel.org>, jgross@...e.com, boris.ostrovsky@...cle.com, konrad.wilk@...cle.com, xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org, Stefano Stabellini <stefano.stabellini@...inx.com> Subject: Re: [PATCH 09/10] xen/arm: introduce phys/dma translations in xen_dma_sync_for_* On Thu, 21 May 2020, Julien Grall wrote: > > @@ -97,8 +98,7 @@ bool xen_arch_need_swiotlb(struct device *dev, > > phys_addr_t phys, > > dma_addr_t dev_addr) > > { > > - unsigned int xen_pfn = XEN_PFN_DOWN(phys); > > - unsigned int bfn = XEN_PFN_DOWN(dev_addr); > > + unsigned int bfn = XEN_PFN_DOWN(dma_to_phys(dev, dev_addr)); > > /* > > * The swiotlb buffer should be used if > > @@ -115,7 +115,7 @@ bool xen_arch_need_swiotlb(struct device *dev, > > * require a bounce buffer because the device doesn't support coherent > > * memory and we are not able to flush the cache. > > */ > > - return (!hypercall_cflush && (xen_pfn != bfn) && > > + return (!hypercall_cflush && !pfn_valid(bfn) && > > I believe this change is incorrect. The bfn is a frame based on Xen page > granularity (always 4K) while pfn_valid() is expecting a frame based on the > Kernel page granularity. Given that kernel granularity >= xen granularity it looks like it would be safe to use PFN_DOWN instead of XEN_PFN_DOWN: unsigned int bfn = PFN_DOWN(dma_to_phys(dev, dev_addr)); return (!hypercall_cflush && !pfn_valid(bfn) &&
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