Re: [PATCH v6 07/33] iommu: Avoid reallocate default domain for a group

From: Will Deacon <will@kernel.org>
To: Yong Wu <yong.wu@mediatek.com>
Cc: youlin.pei@mediatek.com, devicetree@vger.kernel.org,
	Nicolas Boichat <drinkcat@chromium.org>,
	srv_heupstream@mediatek.com, chao.hao@mediatek.com,
	Joerg Roedel <joro@8bytes.org>,
	linux-kernel@vger.kernel.org, Evan Green <evgreen@chromium.org>,
	Tomasz Figa <tfiga@google.com>,
	iommu@lists.linux-foundation.org,
	Rob Herring <robh+dt@kernel.org>,
	linux-mediatek@lists.infradead.org,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	anan.sun@mediatek.com, Robin Murphy <robin.murphy@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 07/33] iommu: Avoid reallocate default domain for a group
Date: Fri, 29 Jan 2021 08:47:31 +0000	[thread overview]
Message-ID: <20210129084731.GA3998@willie-the-truck> (raw)
In-Reply-To: <1611885162.5302.19.camel@mhfsdcap03>

On Fri, Jan 29, 2021 at 09:52:42AM +0800, Yong Wu wrote:
> On Thu, 2021-01-28 at 21:14 +0000, Will Deacon wrote:
> > On Thu, Jan 28, 2021 at 09:10:20PM +0000, Will Deacon wrote:
> > > On Wed, Jan 27, 2021 at 05:39:16PM +0800, Yong Wu wrote:
> > > > On Tue, 2021-01-26 at 22:23 +0000, Will Deacon wrote:
> > > > > On Mon, Jan 11, 2021 at 07:18:48PM +0800, Yong Wu wrote:
> > > > > > If group->default_domain exists, avoid reallocate it.
> > > > > > 
> > > > > > In some iommu drivers, there may be several devices share a group. Avoid
> > > > > > realloc the default domain for this case.
> > > > > > 
> > > > > > Signed-off-by: Yong Wu <yong.wu@mediatek.com>
> > > > > > ---
> > > > > >  drivers/iommu/iommu.c | 3 ++-
> > > > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > > > > 
> > > > > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > > > > > index 3d099a31ddca..f4b87e6abe80 100644
> > > > > > --- a/drivers/iommu/iommu.c
> > > > > > +++ b/drivers/iommu/iommu.c
> > > > > > @@ -266,7 +266,8 @@ int iommu_probe_device(struct device *dev)
> > > > > >  	 * support default domains, so the return value is not yet
> > > > > >  	 * checked.
> > > > > >  	 */
> > > > > > -	iommu_alloc_default_domain(group, dev);
> > > > > > +	if (!group->default_domain)
> > > > > > +		iommu_alloc_default_domain(group, dev);
> > > > > 
> > > > > I don't really get what this achieves, since iommu_alloc_default_domain()
> > > > > looks like this:
> > > > > 
> > > > > static int iommu_alloc_default_domain(struct iommu_group *group,
> > > > > 				      struct device *dev)
> > > > > {
> > > > > 	unsigned int type;
> > > > > 
> > > > > 	if (group->default_domain)
> > > > > 		return 0;
> > > > > 
> > > > > 	...
> > > > > 
> > > > > in which case, it should be fine?
> > > > 
> > > > oh. sorry, I overlooked this. the current code is enough.
> > > > I will remove this patch. and send the next version in this week.
> > > > Thanks very much.
> > > 
> > > Actually, looking at this again, if we're dropping this patch and patch 6
> > > just needs the kfree() moving about, then there's no need to repost. The
> > > issue that Robin and Paul are discussing can be handled separately.
> > 
> > Argh, except that this version of the patches doesn't apply :)
> > 
> > So after all that, please go ahead and post a v7 ASAP based on this branch:
> > 
> > https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/log/?h=for-joerg/mtk
> 
> After confirm with Tomasz, He still need some time to take a look at v6.
> 
> thus I need wait some time to send v7 after his feedback.
> 
> Thanks for your comment. and Thanks Tomasz for the review.

Ok, but please be aware that I'm planning to send my queue to Joerg on
Monday, so if it doesn't show up today then it will miss 5.12.

Will

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