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Subject: Re: [PATCH v2] xen/hvc: replace BUG_ON() with negative return value
To:     Juergen Gross <jgross@suse.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
References: <20210707091045.460-1-jgross@suse.com>
From:   Jan Beulich <jbeulich@suse.com>
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On 07.07.2021 11:10, Juergen Gross wrote:
> Xen frontends shouldn't BUG() in case of illegal data received from
> their backends. So replace the BUG_ON()s when reading illegal data from
> the ring page with negative return values.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>

> --- a/drivers/tty/hvc/hvc_xen.c
> +++ b/drivers/tty/hvc/hvc_xen.c
> @@ -86,7 +86,11 @@ static int __write_console(struct xencons_info *xencons,
>  	cons = intf->out_cons;
>  	prod = intf->out_prod;
>  	mb();			/* update queue values before going on */

Largely unrelated note: While in general the barriers here may want
switching to virt_*mb(), this particular one looks to be too heavy
anyway: a read barrier is all that's needed here afaict, just like
there's only a write barrier between ring contents and producer
writing in __write_console().

And btw, since I've got puzzled by the linuxppc-dev@ in the recipients
list, I did look up relevant entries in ./MAINTAINERS. Shouldn't the
file be part of "XEN HYPERVISOR INTERFACE"?

Jan