linux-kernel - Re: [PATCH 0/4] vfio-pci/zdev: Fixing s390 vfio-pci ISM support

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Message-ID: <d44a5da8-1cb9-8b1c-ef48-caea4bda2fa8@linux.ibm.com>
Date:   Wed, 20 Jan 2021 10:02:08 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        alex.williamson@...hat.com, cohuck@...hat.com,
        schnelle@...ux.ibm.com
Cc:     borntraeger@...ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] vfio-pci/zdev: Fixing s390 vfio-pci ISM support



On 1/19/21 9:02 PM, Matthew Rosato wrote:
> Today, ISM devices are completely disallowed for vfio-pci passthrough as
> QEMU will reject the device due to an (inappropriate) MSI-X check.
> However, in an effort to enable ISM device passthrough, I realized that the
> manner in which ISM performs block write operations is highly incompatible
> with the way that QEMU s390 PCI instruction interception and
> vfio_pci_bar_rw break up I/O operations into 8B and 4B operations -- ISM
> devices have particular requirements in regards to the alignment, size and
> order of writes performed.  Furthermore, they require that legacy/non-MIO
> s390 PCI instructions are used, which is also not guaranteed when the I/O
> is passed through the typical userspace channels.
> 
> As a result, this patchset proposes a new VFIO region to allow a guest to
> pass certain PCI instruction intercepts directly to the s390 host kernel
> PCI layer for execution, pinning the guest buffer in memory briefly in
> order to execute the requested PCI instruction.
> 
> Changes from RFC -> v1:
> - No functional changes, just minor commentary changes -- Re-posting along
> with updated QEMU set.
> 

Hi,

there are is a concerns about this patch series:
As the title says it is strongly related to ISM hardware.

Why being so specific?

Regards,
Pierre

-- 
Pierre Morel
IBM Lab Boeblingen