[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Question about PLATFORM_QUIRK_DOM0_MAPPING_11
On Wed, 2013-09-04 at 20:30 +0800, Chen Baozi wrote: > On Sep 3, 2013, at 8:49 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote: > > > On Tue, 2013-09-03 at 20:41 +0800, Chen Baozi wrote: > >> When porting Xen on OMAP5, we need to add .quirks handler which > >> returns the PLATFORM_QUIRK_DOM0_MAPPING_11. I have read the related > >> set_memory_reg() in domain_build.c. And My question is in which case > >> we don't need to return PLATFORM_QUIRK_DOM0_MAPPING_11 in .quirks and > >> how Xen handles that case to populate right P2M to dom0? > > > > DOM0_MAPPING_11 is a workaround for lack of an iommu, either in hardware > > (e.g. ARM SMMU) or in software (e.g. Stefano's swiotlb patches). In the > > short term it seems like Stefano's patches are going to be ready before > > we have an SMMU driver in the hypervisor. > > > > In any case DOM0_MAPPING_11 will hopefully go away before too long. > > Thanks a lot. And one more question :P > > The reason that we cannot boot successfully without DOM0_MAPPING_11 on > OMAP5 is because in that case the physical address dom0 writes to DMA > controller is intermediate physical address rather than physical address. > If we did the 1:1 mapping, the IPA of dom0 is then equal to the PA, in > which case the DMA can work properly in dom0. Is this the right explanation > why we need PLATFORM_QUIRK_DOM0_MAPPING_11 without either SMMU or swiotlb? Correct. BTW, ballooning dom0 tends to destroy the 1:1 map, so it's by no means a perfect bandaid. Ian. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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