Re: [RFC PATCH V2] vhost: don't use kmap() to log dirty pages

[Jason Wang]

On 2019/5/10 äå12:48, Jason Wang wrote:
> On 2019/5/10 äå10:59, Jason Wang wrote:
> > > > Â ÂÂÂÂÂ r = get_user_pages_fast(log, 1, 1, &page);
> > > OK so the trick is that page is pinned so you don't expect
> > > arch_futex_atomic_op_inuser below to fail. get_user_pages_fast
> > > guarantees page is not going away but does it guarantee PTE won't be
> > > invaidated or write protected?
> >
> >
> > Good point, then I think we probably need to do manual fixup through 
> > fixup_user_fault() if arch_futex_atomic_op_in_user() fail. 
>
>
> This looks like a overkill, we don't need to atomic environment here 
> actually. Instead, just keep pagefault enabled should work. So just 
> introduce arch_futex_atomic_op_inuser_inatomic() variant with 
> pagefault disabled there just for futex should be sufficient.
>
> Thanks


Ok, instead of using tricks, I think we can gracefully fallback to a 
get_user()/put_user() pair protected by a mutex.

Let me post a non-rfc version for this.

Thanks