From: Jason Gunthorpe <jgg@nvidia.com>
To: Alex Williamson <alex.williamson@nvidia.com>
Cc: Alex Williamson <alex@shazbot.org>, kvm <kvm@vger.kernel.org>,
Kevin Tian <kevin.tian@intel.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Yishai Hadas <yishaih@nvidia.com>,
rananta@google.com, stable@vger.kernel.org
Subject: Re: [PATCH v2 1/2] vfio/pci: Fix racy bitfields and tighten struct layout
Date: Tue, 12 May 2026 10:18:12 -0300 [thread overview]
Message-ID: <20260512131812.GA7655@nvidia.com> (raw)
In-Reply-To: <20260511221609.3837652-2-alex.williamson@nvidia.com>
On Mon, May 11, 2026 at 04:16:02PM -0600, Alex Williamson wrote:
> Bitfield operations are not atomic, they use a read-modify-write
> pattern, therefore we should be careful not to pack bitfields that
> can be concurrently updated into the same storage unit.
>
> The split fields (virq_disabled, bardirty, pm_intx_masked,
> pm_runtime_engaged, sriov_pwr_active) are mutated post-init from
> contexts that don't serialize against the other writers in the same
> storage unit, so a bitfield RMW could drop an adjacent field's
> update. The remaining bitfields are touched only during probe or
> close where no concurrent writer exists, so they stay packed.
>
> While reordering, place virq_disabled and bardirty earlier to fill
> an existing alignment hole.
I feel like a comment is needed here for the various bool groupings
'write locked by XX' or something?
Jason
next prev parent reply other threads:[~2026-05-12 13:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-11 22:16 [PATCH v2 0/2] vfio: Fix racy bitfields and tighten struct layout Alex Williamson
2026-05-11 22:16 ` [PATCH v2 1/2] vfio/pci: " Alex Williamson
2026-05-12 13:17 ` David Laight
2026-05-12 13:26 ` Alex Williamson
2026-05-12 13:18 ` Jason Gunthorpe [this message]
2026-05-11 22:16 ` [PATCH v2 2/2] vfio/mlx5: " Alex Williamson
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