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Subject: Re: [PATCH v2] xen/hvc: replace BUG_ON() with negative return value
To:     Jan Beulich <jbeulich@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>
 <9e45c5f8-0ac0-e1bb-4703-838679285e80@suse.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <dd32b09b-7345-664b-165d-dfb30c285448@suse.com>
Date:   Wed, 7 Jul 2021 12:40:54 +0200
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From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <jbeulich@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
Message-ID: <dd32b09b-7345-664b-165d-dfb30c285448@suse.com>
Subject: Re: [PATCH v2] xen/hvc: replace BUG_ON() with negative return value
References: <20210707091045.460-1-jgross@suse.com>
 <9e45c5f8-0ac0-e1bb-4703-838679285e80@suse.com>
In-Reply-To: <9e45c5f8-0ac0-e1bb-4703-838679285e80@suse.com>

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On 07.07.21 11:57, Jan Beulich wrote:
> 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 fro=
m
>> the ring page with negative return values.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>=20
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
>=20
>> --- 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 *xen=
cons,
>>   	cons =3D intf->out_cons;
>>   	prod =3D intf->out_prod;
>>   	mb();			/* update queue values before going on */
>=20
> 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().

I agree.

> 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"?

I wouldn't mind. Greg, Jiri, what do you think?


Juergen

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