[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v5 11/13] xen: introduce xen_alloc/free_coherent_pages
On Fri, Sep 06, 2013 at 03:59:02PM +0100, Stefano Stabellini wrote: > On Fri, 6 Sep 2013, Catalin Marinas wrote: > > On Thu, Sep 05, 2013 at 05:43:33PM +0100, Stefano Stabellini wrote: > > > On Thu, 5 Sep 2013, Catalin Marinas wrote: > > > > On Thu, Aug 29, 2013 at 07:32:32PM +0100, Stefano Stabellini wrote: > > > > > xen_swiotlb_alloc_coherent needs to allocate a coherent buffer for cpu > > > > > and devices. On native x86 and ARMv8 is sufficient to call > > > > > __get_free_pages in order to get a coherent buffer, while on ARM we > > > > > need > > > > > to call arm_dma_ops.alloc. > > > > > > > > Don't bet on this for ARMv8. It's not mandated for the architecture, so > > > > at some point some SoC will require non-cacheable buffers for coherency. > > > > > > I see. > > > Would it be better if I implemented xen_alloc_coherent_pages on armv8 by > > > calling arm64_swiotlb_dma_ops.alloc? > > > > What does this buffer do exactly? Is it allocated by guests? > > It is allocated by Dom0 to do DMA to/from a device. > It is the buffer that is going to be returned by dma_map_ops.alloc to > the caller: > > On x86: > dma_map_ops.alloc -> xen_swiotlb_alloc_coherent -> xen_alloc_coherent_pages > -> __get_free_pages > > On ARM: > dma_map_ops.alloc -> xen_swiotlb_alloc_coherent -> xen_alloc_coherent_pages > -> arm_dma_ops.alloc > > On ARM64 > dma_map_ops.alloc -> xen_swiotlb_alloc_coherent -> xen_alloc_coherent_pages > -> ???? OK, I'm getting more confused. Do all the above calls happen in the guest, Dom0, or a mix? -- Catalin _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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