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

From: Stefano Stabellini <sstabellini@kernel.org>
To: Jan Beulich <JBeulich@suse.com>
Cc: anthony.perard@citrix.com,
	xen-devel <xen-devel@lists.xenproject.org>,
	Paul Durrant <paul.durrant@citrix.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	qemu-devel@nongnu.org
Subject: Re: [PATCH v2 1/3] xen: fix quad word bufioreq handling
Date: Mon, 28 Nov 2016 11:21:49 -0800 (PST)	[thread overview]
Message-ID: <alpine.DEB.2.10.1611281121400.21858__12121.5439787649$1480360983$gmane$org@sstabellini-ThinkPad-X260> (raw)
In-Reply-To: <58381B15020000780012226B@prv-mh.provo.novell.com>

On Fri, 25 Nov 2016, Jan Beulich wrote:
> 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>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


> v2: Bail (using hw_error()) instead of just breaking the loop.
> 
> --- 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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