Messages in this thread | | | Date | Tue, 09 Sep 2008 07:47:07 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH 1 of 7] x86: add _PAGE_IOMAP pte flag for IO mappings |
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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?
Also, _PAGE_SPECIAL is also shared with _PAGE_CPA_TEST, which is only used on kernel mappings, so they can co-exist happily.
Is _PAGE_IOMAP at all useful for device passthrough in kvm?
J
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