[Qemu-devel] Re: POLL: Why do you use kqemu?

[Avi Kivity <avi@redhat.com>]

Jan Kiszka wrote:
> And the fact that kqemu has to use tcg in order to achieve a reasonable
> performance is rather a disadvantage. The complexity and overhead for
> synchronizing tcg with the in-kernel accelerator is enormous. If there
> were a feasible way to overcome this with kqemu, it would benefit a lot.
> But unfortunately there is none (given you don't want to invest
> reasonable efforts).
>   

Note that kvm suffers from something similar (to a smaller magnitude) as 
well: if a guest pages in its page tables, kvm knows nothing about it 
and will thus have outdated shadows.  To date we haven't encountered a 
problem with it, but it's conceivable.  I think Windows can page its 
page tables, but maybe it's disabled by default, or maybe it doesn't dma 
directly into the page tables.

Not sure how to fix.  Maybe write protect the host page tables when we 
shadow a page table, and get an mmu notifier to tell us when its made 
writable?  Seems expensive.  Burying head in sand is much easier.

-- 
error compiling committee.c: too many arguments to function