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From: Vincent Whitchurch <vincent.whitchurch@axis.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org"
	<virtualization@lists.linux-foundation.org>,
	kernel <kernel@axis.com>
Subject: Re: [PATCH] vhost: add support for mandatory barriers
Date: Tue, 24 Aug 2021 09:23:06 +0200	[thread overview]
Message-ID: <20210824072306.GA29073@axis.com> (raw)
In-Reply-To: <20210823171609-mutt-send-email-mst@kernel.org>

On Mon, Aug 23, 2021 at 11:19:56PM +0200, Michael S. Tsirkin wrote:
> On Mon, Aug 23, 2021 at 10:14:37AM +0200, Vincent Whitchurch wrote:
> > vhost always uses SMP-conditional barriers, but these may not be
> > sufficient when vhost is used to communicate between heterogeneous
> > processors in an AMP configuration, especially since they're NOPs on
> > !SMP builds.
> > 
> > To solve this, use the virtio_*() barrier functions and ask them for
> > non-weak barriers if requested by userspace.
> > 
> > Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> 
> I am inclined to say let's (ab)use VIRTIO_F_ORDER_PLATFORM for this.
> Jason what do you think?

OK, thanks, I'll look into that.

> Also is the use of DMA variants really the intended thing here? Could
> you point me at some examples please?

I'm using this on an ARM-based SoC.  The main processor is a Cortex-A53
(arm64) and this processor runs the virtio drivers.  The SoC also has
another processor which is a Cortex-A5 (arm32) and this processor runs
the virtio device end using vhost.  There is no coherency between these
two processors and to each other they look like any other DMA-capable
hardware.
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WARNING: multiple messages have this Message-ID (diff)
From: Vincent Whitchurch <vincent.whitchurch@axis.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>, kernel <kernel@axis.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] vhost: add support for mandatory barriers
Date: Tue, 24 Aug 2021 09:23:06 +0200	[thread overview]
Message-ID: <20210824072306.GA29073@axis.com> (raw)
In-Reply-To: <20210823171609-mutt-send-email-mst@kernel.org>

On Mon, Aug 23, 2021 at 11:19:56PM +0200, Michael S. Tsirkin wrote:
> On Mon, Aug 23, 2021 at 10:14:37AM +0200, Vincent Whitchurch wrote:
> > vhost always uses SMP-conditional barriers, but these may not be
> > sufficient when vhost is used to communicate between heterogeneous
> > processors in an AMP configuration, especially since they're NOPs on
> > !SMP builds.
> > 
> > To solve this, use the virtio_*() barrier functions and ask them for
> > non-weak barriers if requested by userspace.
> > 
> > Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> 
> I am inclined to say let's (ab)use VIRTIO_F_ORDER_PLATFORM for this.
> Jason what do you think?

OK, thanks, I'll look into that.

> Also is the use of DMA variants really the intended thing here? Could
> you point me at some examples please?

I'm using this on an ARM-based SoC.  The main processor is a Cortex-A53
(arm64) and this processor runs the virtio drivers.  The SoC also has
another processor which is a Cortex-A5 (arm32) and this processor runs
the virtio device end using vhost.  There is no coherency between these
two processors and to each other they look like any other DMA-capable
hardware.

  parent reply	other threads:[~2021-08-24  7:23 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-23  8:14 [PATCH] vhost: add support for mandatory barriers Vincent Whitchurch
2021-08-23  8:14 ` Vincent Whitchurch
2021-08-23 21:19 ` Michael S. Tsirkin
2021-08-23 21:19   ` Michael S. Tsirkin
2021-08-24  2:56   ` Jason Wang
2021-08-24  2:56     ` Jason Wang
2021-08-24  7:23   ` Vincent Whitchurch [this message]
2021-08-24  7:23     ` Vincent Whitchurch

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