linux-kernel - Re: [PATCH v2] hvc/xen: prevent concurrent accesses to the shared ring

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Message-ID: <25fd6eca-a7c7-9b08-80a0-a0c998df664a@suse.com>
Date:   Fri, 17 Mar 2023 14:23:16 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Roger Pau Monne <roger.pau@...rix.com>,
        linux-kernel@...r.kernel.org
Cc:     xen-devel@...ts.xenproject.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Jan Beulich <jbeulich@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Chris Wright <chrisw@...s-sol.org>,
        Ingo Molnar <mingo@...e.hu>,
        Jeremy Fitzhardinge <jeremy@...source.com>,
        Olof Johansson <olof@...om.net>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] hvc/xen: prevent concurrent accesses to the shared
 ring

On 30.11.22 16:09, Roger Pau Monne wrote:
> The hvc machinery registers both a console and a tty device based on
> the hv ops provided by the specific implementation.  Those two
> interfaces however have different locks, and there's no single locks
> that's shared between the tty and the console implementations, hence
> the driver needs to protect itself against concurrent accesses.
> Otherwise concurrent calls using the split interfaces are likely to
> corrupt the ring indexes, leaving the console unusable.
> 
> Introduce a lock to xencons_info to serialize accesses to the shared
> ring.  This is only required when using the shared memory console,
> concurrent accesses to the hypercall based console implementation are
> not an issue.
> 
> Note the conditional logic in domU_read_console() is slightly modified
> so the notify_daemon() call can be done outside of the locked region:
> it's an hypercall and there's no need for it to be done with the lock
> held.
> 
> Fixes: b536b4b96230 ('xen: use the hvc console infrastructure for Xen console')
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen


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