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Date:   Sat, 18 Apr 2020 14:10:22 +0200
From:   Joerg Roedel <joro@8bytes.org>
To:     Qian Cai <cai@lca.pw>
Cc:     iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] iommu/amd: fix a race in fetch_pte()
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On Thu, Apr 16, 2020 at 09:42:41PM -0400, Qian Cai wrote:
> So, this is still not enough that would still trigger storage driver offline under
> memory pressure for a bit longer. It looks to me that in fetch_pte() there are
> could still racy?

Yes, your patch still looks racy. You need to atomically read
domain->pt_root to a stack variable and derive the pt_root pointer and
the mode from that variable instead of domain->pt_root directly. If you
read the domain->pt_root twice there could still be an update between
the two reads.
Probably the lock in increase_address_space() can also be avoided if
pt_root is updated using cmpxchg()?

Regards,

	Joerg