Re: [RFC PATCH 03/19] vfio/pci: Add PCI recovery access guards

[sashiko-bot@kernel.org]

> Add a pair of helpers to wrap each operation which touches the device.
> access_begin() takes recovery_lock for reading and refuses if the device
> is not open, or if recovery is blocking access. The callers come in later
> patches.
> 
> access_end() drops the lock without looking at the recovery state, so
> only call it after access_begin() returned 0. On failure the lock is
> already gone. Both helpers key off pci_recovery_supported, which is
> fixed for the lifetime of the device, so the pair stays balanced.
> 
> The lock is taken even when userspace has not enabled recovery. Enabling
> takes recovery_lock for writing, which waits for anything already in
> flight. Without that, an operation which started before enable could
> still be touching the device when the first error arrives, and there would
> be nothing to wait on.
> 
> access_blocked is checked either way. Nothing sets it yet, so nothing
> which works today gets rejected.
> 
> The cost is one rwsem acquire per guarded access on devices that never
> turn recovery on. For BAR traffic that is once per width-sized access,
> alongside the memory_lock read already taken there.
> 
> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260901093217.8539-1-skolothumtho@nvidia.com?part=3