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xen-devel
Re: [Xen-devel] Regarding page table management changes from Xen v1to Xe
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.
-- Keir
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