> -----Original Message-----
> From: Manish Honap <mhonap@nvidia.com>
> Sent: 01 June 2026 08:56
> To: Jonathan Cameron <jic23@kernel.org>
> Cc: Alex Williamson <alwilliamson@nvidia.com>; Shameer Kolothum Thodi
> <skolothumtho@nvidia.com>; Ankit Agrawal <ankita@nvidia.com>;
> mst@redhat.com; imammedo@redhat.com; anisinha@redhat.com;
> eric.auger@redhat.com; peter.maydell@linaro.org;
> shannon.zhaosl@gmail.com; jonathan.cameron@huawei.com;
> fan.ni@samsung.com; pbonzini@redhat.com; richard.henderson@linaro.org;
> marcel.apfelbaum@gmail.com; clg@redhat.com; cohuck@redhat.com;
> dave.jiang@intel.com; alejandro.lucero-palau@amd.com; Vikram Sethi
> <vsethi@nvidia.com>; Neo Jia <cjia@nvidia.com>; Tarun Gupta (SW-GPU)
> <targupta@nvidia.com>; Zhi Wang <zhiw@nvidia.com>; Krishnakant Jaju
> <kjaju@nvidia.com>; linux-cxl@vger.kernel.org; kvm@vger.kernel.org; qemu-
> devel@nongnu.org; qemu-arm@nongnu.org; Manish Honap
> <mhonap@nvidia.com>
> Subject: RE: [RFC 0/9] QEMU: CXL Type-2 device passthrough via vfio-pci
> 

[...]

> > > pxb-cxl bridges had no _DSM method. Without _DSM function 5 the OS
> > > defaults to treating PCI configuration as reassignable.
> >
> > That one is annoyingly controversial. I see you have Shameer's patch
> > so he can go into history of why. I tried to land that in the past and
> > I was far from the first.
> 
> okay, I will check this part for additional details.

I guess the concern here is the QEMU regression reported with certain
devices with legacy IO port BARs having issues on arm64 when _DSM #5 is
specified:
https://lore.kernel.org/all/20210724185234.GA2265457@roeck-us.net/

For accel SMMUv3 this is fine as we restrict the devices to vfio-pci only.
One option, until there is a proper fix in the Linux kernel or EDK2, might
be to maintain a checklist so that devices known to have issues are not
attached when _DSM #5 is advertised.

Thanks,
Shameer