linux-kernel - Re: [PATCH 1/7] xen/events: reset affinity of 2-level event initially

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 6 Feb 2021 11:20:16 +0000
From:   Julien Grall <julien@....org>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/7] xen/events: reset affinity of 2-level event initially

Hi Juergen,

On 06/02/2021 10:49, Juergen Gross wrote:
> When creating a new event channel with 2-level events the affinity
> needs to be reset initially in order to avoid using an old affinity
> from earlier usage of the event channel port.
> 
> The same applies to the affinity when onlining a vcpu: all old
> affinity settings for this vcpu must be reset. As percpu events get
> initialized before the percpu event channel hook is called,
> resetting of the affinities happens after offlining a vcpu (this is
> working, as initial percpu memory is zeroed out).
> 
> Cc: stable@...r.kernel.org
> Reported-by: Julien Grall <julien@....org>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>   drivers/xen/events/events_2l.c | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/xen/events/events_2l.c b/drivers/xen/events/events_2l.c
> index da87f3a1e351..23217940144a 100644
> --- a/drivers/xen/events/events_2l.c
> +++ b/drivers/xen/events/events_2l.c
> @@ -47,6 +47,16 @@ static unsigned evtchn_2l_max_channels(void)
>   	return EVTCHN_2L_NR_CHANNELS;
>   }
>   
> +static int evtchn_2l_setup(evtchn_port_t evtchn)
> +{
> +	unsigned int cpu;
> +
> +	for_each_online_cpu(cpu)
> +		clear_bit(evtchn, BM(per_cpu(cpu_evtchn_mask, cpu)));

The bit corresponding to the event channel can only be set on a single 
CPU. Could we avoid the loop and instead clear the bit while closing the 
port?

Cheers,

-- 
Julien Grall