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

From: Paul Durrant <Paul.Durrant@citrix.com>
To: Jan Beulich <JBeulich@suse.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Cc: Anthony Perard <anthony.perard@citrix.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [Qemu-devel] [PATCH v2 1/3] xen: fix quad word bufioreq handling
Date: Fri, 25 Nov 2016 10:08:14 +0000	[thread overview]
Message-ID: <9f17b0ea9b964909be1be79d5786ea41@AMSPEX02CL03.citrite.net> (raw)
In-Reply-To: <58381B15020000780012226B@prv-mh.provo.novell.com>

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: 25 November 2016 10:06
> To: qemu-devel@nongnu.org
> Cc: Anthony Perard <anthony.perard@citrix.com>; Paul Durrant
> <Paul.Durrant@citrix.com>; Stefano Stabellini <sstabellini@kernel.org>; xen-
> devel <xen-devel@lists.xenproject.org>
> 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@huawei.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> v2: Bail (using hw_error()) instead of just breaking the loop.

LGTM.

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

> 
> --- 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;
> 
> 