Re: [RFC PATCH 09/19] vfio/pci: Serialize interrupt operations with recovery

[sashiko-bot@kernel.org]

> Hold recovery_lock for reading around INTx, MSI and MSI-X capability
> queries and configuration changes. ERR and REQ are software-only indexes
> and stay available while recovery blocks device access. INTx is covered
> by the same test even though its count comes from the virtual config
> space, so that one rule applies to every index which can reach hardware.
> 
> The test is on the index alone, so a blocked device also refuses the few
> requests on those indexes which would not have touched it: signalling an
> eventfd for test purposes, and adding or removing the virqfd behind INTx
> masking. Both return -EIO until access is unblocked, which for a
> non-fatal error is the time the host takes to log it. Reading the flags
> or the count of a request is not enough to tell whether it reaches the
> device, and refusing a few extra requests for the length of an error
> event is cheaper than getting that classification wrong.
> 
> Copy the IRQ payload from userspace before taking recovery_lock. The copy
> can fault, and with userfaultfd the fault is serviced by userspace, so
> holding the lock across it would let a user stall error_detected() for as
> long as it likes. The count read and the interrupt operation each take
> the lock for themselves.
> 
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>

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

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