linux-kernel - Re: [PATCH 6/7] xen/evtch: use smp barriers for user event ring

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Message-ID: <dfa40af0-2706-2540-c59a-6593c1c0553a@suse.com>
Date:   Mon, 8 Feb 2021 10:50:11 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Andrew Cooper <andrew.cooper3@...rix.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 6/7] xen/evtch: use smp barriers for user event ring

On 08.02.2021 10:44, Andrew Cooper wrote:
> On 06/02/2021 10:49, Juergen Gross wrote:
>> The ring buffer for user events is used in the local system only, so
>> smp barriers are fine for ensuring consistency.
>>
>> Reported-by: Andrew Cooper <andrew.cooper3@...rix.com>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
> 
> These need to be virt_* to not break in UP builds (on non-x86).

Initially I though so, too, but isn't the sole vCPU of such a
VM getting re-scheduled to a different pCPU in the hypervisor
an implied barrier anyway?

Jan