Re: [PATCH bpf-next 02/15] xsk: add user memory registration support sockopt

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Apr 23, 2018 at 10:00:15PM +0200, Björn Töpel wrote:
> 2018-04-23 18:18 GMT+02:00 Michael S. Tsirkin <mst@redhat.com>:
> 
> [...]
> 
> >> +static void xdp_umem_unpin_pages(struct xdp_umem *umem)
> >> +{
> >> +     unsigned int i;
> >> +
> >> +     if (umem->pgs) {
> >> +             for (i = 0; i < umem->npgs; i++)
> >
> > Since you pin them with FOLL_WRITE, I assume these pages
> > are written to.
> > Don't you need set_page_dirty_lock here?
> >
> 
> Hmm, I actually *removed* it from the RFC V2, but after doing some
> homework, I think you're right. Thanks for pointing this out!
> 
> Thinking more about this; This function is called from sk_destruct,
> and in the Tx case the sk_destruct can be called from interrupt
> context, where set_page_dirty_lock cannot be called.
> 
> Are there any preferred ways of solving this? Scheduling the whole
> xsk_destruct call to a workqueue is one way (I think). Any
> cleaner/better way?
> 
> [...]

Defer unpinning pages until the next tx call?


> >> +static int __xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
> >> +{
> >> +     u32 frame_size = mr->frame_size, frame_headroom = mr->frame_headroom;
> >> +     u64 addr = mr->addr, size = mr->len;
> >> +     unsigned int nframes;
> >> +     int size_chk, err;
> >> +
> >> +     if (frame_size < XDP_UMEM_MIN_FRAME_SIZE || frame_size > PAGE_SIZE) {
> >> +             /* Strictly speaking we could support this, if:
> >> +              * - huge pages, or*
> >
> > what does "or*" here mean?
> >
> 
> Oops, I'll change to just 'or' in the next revision.
> 
> 
> Thanks!
> Björn