Re: [Xen-devel] writable pagetable

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> On the subject of writable pagetables, is it a performance thing? I've
> always said 'no' because I don't know what it does and went with the
> philosophy of "if it ain't broke...".

It's a 'minimal changes to the OS' thing. The old batching interface
meant that, until you explicitly flushed your update batch, subsequent
reads of 'updated' page table entries would return the old
contents. To avoid introducing OS bugs we had to sprinkle explicit
flushes around the Linux 2.4 generic MM code. We avoid this in 2.6 by
allowing th eguest to directly write its page tables, in place.

 -- Keir


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