linux-kernel - Re: [PATCH 1/1] iommu: Avoid races around default domain allocations

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Message-ID: <20240208011305.GM31743@ziepe.ca>
Date: Wed, 7 Feb 2024 21:13:05 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Robin Murphy <robin.murphy@....com>
Cc: Nikhil V <quic_nprakash@...cinc.com>, Will Deacon <will@...nel.org>,
	Joerg Roedel <joro@...tes.org>,
	Charan Teja Kalla <quic_charante@...cinc.com>,
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu: Avoid races around default domain allocations

On Thu, Feb 08, 2024 at 12:04:44AM +0000, Robin Murphy wrote:
> > Frankly, I'd suggest just proposing the necessary (and tested)
> > upstream patches to 6.1, however large they are, and see what Greg and
> > Sasha say. This is the usual working model they have, as I understand
> > it.
> 
> To be blunt, hell no. Stable is far enough from its namesake already; the
> ongoing bordering-on-ridiculous brokenness of your mainline changes where

What on earth are you even talking about? POWER?

> That said, I also don't think there would be any harm in applying this to
> mainline as a belt-and-braces thing either,

Really?

Now that you've made me look, this patch breaks the
iommu_group_store_type() flow both on latest and on v6.1 from what I
can see.

On v6.1:

iommu_change_dev_def_domain():
  
        prev_dom = group->default_domain;
        if (!prev_dom) {
                ret = -EINVAL;
                goto out;
        }
[..]
        /* Sets group->default_domain to the newly allocated domain */
        ret = iommu_group_alloc_default_domain(dev->bus, group, type);
        if (ret)
                goto out;

But this patch changes iommu_group_alloc_default_domain() to succeed
always without doing anythiing.

So this patch needs some fixing.

There is a very good reason the stable people don't like boutique patches..

Jason