[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [PATCH 1 of 7] x86: add _PAGE_IOMAP pte flag for IO mappings
Jeremy Fitzhardinge wrote: Avi Kivity wrote:Jeremy Fitzhardinge wrote:Use one of the software-defined PTE bits to indicate that a mapping is intended for an IO address. On native hardware this is irrelevent, since a physical address is a physical address. But in a virtual environment, physical addresses are also virtualized, so there needs to be some way to distinguish between pseudo-physical addresses and actual hardware addresses; _PAGE_IOMAP indicates this intent. By default, __supported_pte_mask masks out _PAGE_IOMAP, so it doesn't even appear in the final pagetable.Could PTE_SPECIAL, added for get_user_pages_really_fast(), be reused for this?I'm not sure; I still don't really understand how _PAGE_SPECIAL gets used, other than being user-mode mapping only. But in principle, _PAGE_IOMAP could be set on both kernel and user mappings (if you direct map a device into a process address space), so I think they would conflict then? It's a "don't refcount me" flag, which is not sematically the same as I/O, but may be close enough. Is _PAGE_IOMAP at all useful for device passthrough in kvm? No. We don't care if a page is an I/O page or RAM (other than refcounting correctness and page attributes, which are handled by other means). -- error compiling committee.c: too many arguments to function _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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