[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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



Keir Fraser wrote:
> That's basically what our _PAGE_IO flag (in our old Linux patchset) means.
> We use it to cause pte_pfn() to return an invalid pfn and hence avoid
> reference counting that way. Since kernel mappings are never reference
> counted (I think?) perhaps we could use _PAGE_SPECIAL even if it is
> restricted to use on user mappings.

Well, _PAGE_IOMAP's most important semantic from Xen's perspective is
that the frame number is considered to already be an MFN and so isn't
converted.  It may be that _PAGE_SPECIAL is also useful for its "no
refcount" properties, but we could set both in that case.

At present we can't set _PAGE_SPECIAL on kernel mappings because we
assume its usermode only, and its shared with _PAGE_CPA_TEST which is
kernel-only.  Most _PAGE_IOMAP mappings are in kernel space, but I
wouldn't discount user mappings if we end up allowing direct access to
passthrough devices.

    J

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.