[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] [patch] more correct pfn_valid()
>-----Original Message----- >From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx] >Sent: Thursday, May 19, 2005 4:23 PM >To: Tian, Kevin > >On 19 May 2005, at 09:14, Tian, Kevin wrote: > >> For this part, I made a mistake to confuse domN and dom0. OK, for >> paravirtualized guest, there's actually no I/O range for domN, since >> the >> front driver in domN will do all things to communicate with backend in >> Dom0. But what about a driver domain which has access to physical >> device, thus need real I/O address? > >We rely on the driver using the dma_coherent/pci_consistent/bus_address >macros for mapping device memory. Originally designed to handle IOMMUs, >it is handy for us to determine places where code is handling real >machine physical addresses rather than pseudophysical addresses. This >gets groans of distaste from the kernel maintainers but has worked >enormously well so far (AGP needed patching separately though). > > -- Keir Thanks for guide. That's really a way to differentiate normal memory and machine memory used for device. After searching the source tree, yes, if all drivers conform to this convention (should be), low level pci-dma interface can adjust guest pfn -> machine pfn mapping to promise contiguous requirement in machine address layer, and also 4G limitation for old DMA driver on new platform. But, this only handles the difference between machine memory and 'physical' memory, not the one between "physical' memory and machine MMIO space. If 'physical' memory is kept continuous whatever memory size is, there'll be some overlap with machine MMIO space anyway. But since your careful design can promise no confusion, then let it since there're already many mixed knowledge in dear paravirtualized domain. :) Thanks, Kevin _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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