linux-kernel - Re: [PATCH] iommu/s390: Make attach succeed when the device was surprise removed

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Message-ID: <f9e38796-bb97-4846-8f4c-b92421cadc2f@linux.ibm.com>
Date: Thu, 4 Sep 2025 16:56:32 -0400
From: Matthew Rosato <mjrosato@...ux.ibm.com>
To: Niklas Schnelle <schnelle@...ux.ibm.com>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc: Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>, Farhan Ali <alifm@...ux.ibm.com>,
        Benjamin Block <bblock@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux.dev
Subject: Re: [PATCH] iommu/s390: Make attach succeed when the device was
 surprise removed

On 9/4/25 4:59 AM, Niklas Schnelle wrote:
> When a PCI device is removed with surprise hotplug, there may still be
> attempts to attach the device to the default domain as part of tear down
> via (__iommu_release_dma_ownership()), or because the removal happens
> during probe (__iommu_probe_device()). In both cases zpci_register_ioat()
> fails with a cc value indicating that the device handle is invalid. This
> is because the device is no longer part of the instance as far as the
> hypervisor is concerned.
> 
> Currently this leads to an error return and s390_iommu_attach_device()
> fails. This triggers the WARN_ON() in __iommu_group_set_domain_nofail()
> because attaching to the default domain must never fail.
> 
> With the device fenced by the hypervisor no DMAs to or from memory are
> possible and the IOMMU translations have no effect. Proceed as if the
> registration was successful and let the hotplug event handling clean up
> the device.
> 
> This is similar to how devices in the error state are handled since
> commit 59bbf596791b ("iommu/s390: Make attach succeed even if the device
> is in error state") except that for removal the domain will not be
> registered later. This approach was also previously discussed at the
> link.
> 
> Handle both cases, error state and removal, in a helper which checks if
> the error needs to be propagated or ignored. Avoid magic number
> condition codes by using the pre-existing, but never used, defines for
> PCI load/store condition codes and rename them to reflect that they
> apply to all PCI instructions.
> 
> Cc: stable@...r.kernel.org # v6.2
> Link: https://lore.kernel.org/linux-iommu/20240808194155.GD1985367@ziepe.ca/
> Suggested-by: Jason Gunthorpe <jgg@...pe.ca>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---
>  arch/s390/include/asm/pci_insn.h | 10 +++++-----
>  drivers/iommu/s390-iommu.c       | 26 +++++++++++++++++++-------
>  2 files changed, 24 insertions(+), 12 deletions(-)
>

Makes sense to me.

Reviewed-by: Matthew Rosato <mjrosato@...ux.ibm.com>