Re: [PATCH v5 2/2] PCI: s390: Support mmap() of BARs and replace VFIO_PCI_MMAP by a device flag

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Feb 12, 2025 at 04:28:32PM +0100, Niklas Schnelle wrote:
> On s390 there is a virtual PCI device called ISM which has a few
> peculiarities. For one, it presents a 256 TiB PCI BAR whose size leads
> to any attempt to ioremap() the whole BAR failing. This is problematic
> since mapping the whole BAR is the default behavior of for example
> vfio-pci in combination with QEMU and VFIO_PCI_MMAP enabled.
> 
> Even if one tried to map this BAR only partially, the mapping would not
> be usable without extra precautions on systems with MIO support enabled.
> This is because of another oddity, in that this virtual PCI device does
> not support the newer memory I/O (MIO) PCI instructions and legacy PCI
> instructions are not accessible through writeq()/readq() when MIO is in
> use.
> 
> In short the ISM device's BAR is not accessible through memory mappings.
> Indicate this by introducing a new non_mappable_bars flag for the ISM
> device and set it using a PCI quirk. Use this flag instead of the
> VFIO_PCI_MMAP Kconfig option to block mapping with vfio-pci. This was
> the only use of the Kconfig option so remove it. Note that there are no
> PCI resource sysfs files on s390x already as HAVE_PCI_MMAP is currently
> not set. If this were to be set in the future pdev->non_mappable_bars
> can be used to prevent unusable resource files for ISM from being
> created.
> 
> As s390x has no PCI quirk handling add basic support modeled after x86's
> arch/x86/pci/fixup.c and move the ISM device's PCI ID to the common
> header to make it accessible. Also enable CONFIG_PCI_QUIRKS whenever
> CONFIG_PCI is enabled.
> 
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> +++ b/include/linux/pci_ids.h
> @@ -518,6 +518,7 @@
>  #define PCI_DEVICE_ID_IBM_ICOM_V2_ONE_PORT_RVX_ONE_PORT_MDM	0x0251
>  #define PCI_DEVICE_ID_IBM_ICOM_V2_ONE_PORT_RVX_ONE_PORT_MDM_PCIE 0x0361
>  #define PCI_DEVICE_ID_IBM_ICOM_FOUR_PORT_MODEL	0x252
> +#define PCI_DEVICE_ID_IBM_ISM		0x04ED

Use lower-case hex to match other entries.

>  #define PCI_SUBVENDOR_ID_IBM		0x1014
>  #define PCI_SUBDEVICE_ID_IBM_SATURN_SERIAL_ONE_PORT	0x03d4
> 
> -- 
> 2.45.2
>