Re: [PATCH 1 of 7] x86: add _PAGE_IOMAP pte flag for IO mappings

Avi Kivity
2008-09-09T13:32:26Z

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?

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