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xen-devel
Re: [Xen-devel] Regarding page table management changes from Xen v1to Xe
Keir Fraser wrote:
On 26 Apr 2006, at 19:15, Anthony Liguori wrote:
No, these singleton updates on the Linux demand fault path are issued
with the update_va_mapping hypercall. This is possible because the
virtual address that the pte maps is known, so its possible for Xen to
use a linear pagetable to do the update rather than creating an
on-demand mapping to the domain's pagetable page. This is an important
optimization on 32b where Xen address space is tight.
Just to make sure I understand, we do the linear mapping for
performance (so we don't have to keep remapping) but not necessarily
to save VA space since the linear mapping uses a fixed amount of space.
Is there any reason that we would strictly require a linear mapping
(other than it being convenient)?
On 64b we could use the 1:1 mapping of all physmem that Xen has.
Obviously that is infeasible on 32b. In fact the interface (passing a
virtual address) pretty much means we have to use a linear mapping in
both cases.
Couldn't we temporarily map the page table page? Not that we would
actually want to do that. Just trying to confirm my understand.
Regards,
Anthony Liguori
-- Keir
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