Re: [Xen-devel] [PATCH v2 1/3] xen: fix quad word bufioreq handling

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 25 November 2016 10:06
> To: qemu-devel@xxxxxxxxxx
> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>; Paul Durrant
> <Paul.Durrant@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; xen-
> devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Subject: [PATCH v2 1/3] xen: fix quad word bufioreq handling
> 
> We should not consume the second slot if it didn't get written yet.
> Normal writers - i.e. Xen - would not update write_pointer between the
> two writes, but the page may get fiddled with by the guest itself, and
> we're better off avoiding to enter an infinite loop in that case.
> 
> Reported-by: yanghongke <yanghongke@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2: Bail (using hw_error()) instead of just breaking the loop.

LGTM.

Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> 
> --- a/xen-hvm.c
> +++ b/xen-hvm.c
> @@ -1021,6 +1021,9 @@ static int handle_buffered_iopage(XenIOS
>          xen_rmb();
>          qw = (req.size == 8);
>          if (qw) {
> +            if (rdptr + 1 == wrptr) {
> +                hw_error("Incomplete quad word buffered ioreq");
> +            }
>              buf_req = &buf_page->buf_ioreq[(rdptr + 1) %
>                                             IOREQ_BUFFER_SLOT_NUM];
>              req.data |= ((uint64_t)buf_req->data) << 32;
> 
> 


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