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

[Jason Wang]

On 2019/5/14 äå12:42, David Miller wrote:
> From: Jason Wang <jasowang@xxxxxxxxxx>
> Date: Mon, 13 May 2019 01:27:45 -0400
>
> > Vhost log dirty pages directly to a userspace bitmap through GUP and
> > kmap_atomic() since kernel doesn't have a set_bit_to_user()
> > helper. This will cause issues for the arch that has virtually tagged
> > caches. The way to fix is to keep using userspace virtual
> > address. Fortunately, futex has arch_futex_atomic_op_inuser() which
> > could be used for setting a bit to user.
> >
> > Note there're several cases that futex helper can fail e.g a page
> > fault or the arch that doesn't have the support. For those cases, a
> > simplified get_user()/put_user() pair protected by a global mutex is
> > provided as a fallback. The fallback may lead false positive that
> > userspace may see more dirty pages.
> >
> > Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> > Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
> > Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Darren Hart <dvhart@xxxxxxxxxxxxx>
> > Fixes: 3a4d5c94e9593 ("vhost_net: a kernel-level virtio server")
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> I want to see a review from Michael for this change before applying.


No problem, since kbuild spotted an issue. Let me post V2.

Thanks