Re: [patch 2/5] KVM: hypercall based pte updates and TLB flushes

[Avi Kivity <avi@qumranet.com>]

Marcelo Tosatti wrote:
> Hypercall based pte updates are faster than faults, and also allow use
> of the lazy MMU mode to batch operations.
>
> Don't report the feature if two dimensional paging is enabled.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> +/*
> + * We only need to hook operations that are MMU writes.  We hook these so that
> + * we can use lazy MMU mode to batch these operations.  We could probably
> + * improve the performance of the host code if we used some of the information
> + * here to simplify processing of batched writes.
> + */
>   

One option is, if the guest promises never to write to a page table 
directly, is to avoid write protecting guest page tables.  I think the 
shadow code can handle it (since the gfn/spte relationship is maintained 
by shadow code, and doesn't require reading the guest page tables), but 
am not sure.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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