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

Niklas Schnelle
2025-02-12T15:29:17Z

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>
---
arch/s390/Kconfig | 4 +---
arch/s390/pci/Makefile | 2 +-
arch/s390/pci/pci_fixup.c | 23 +++++++++++++++++++++++
drivers/s390/net/ism_drv.c | 1 -
drivers/vfio/pci/Kconfig | 4 ----
drivers/vfio/pci/vfio_pci_core.c | 2 +-
include/linux/pci.h | 1 +
include/linux/pci_ids.h | 1 +
8 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 9c9ec08d78c71b4d227beeafab1b82d6434cb5c7..e48741e001476f765e8aba0037a1b386df393683 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -41,9 +41,6 @@ config AUDIT_ARCH
config NO_IOPORT_MAP
def_bool y

-config PCI_QUIRKS
- def_bool n
-
config ARCH_SUPPORTS_UPROBES
def_bool y

@@ -258,6 +255,7 @@ config S390
select PCI_DOMAINS if PCI
select PCI_MSI if PCI
select PCI_MSI_ARCH_FALLBACKS if PCI_MSI
+ select PCI_QUIRKS if PCI
select SPARSE_IRQ
select SWIOTLB
select SYSCTL_EXCEPTION_TRACE
diff --git a/arch/s390/pci/Makefile b/arch/s390/pci/Makefile
index df73c5182990ad3ae4ed5a785953011feb9a093c..1810e0944a4ed9d31261788f0f6eb341e5316546 100644
--- a/arch/s390/pci/Makefile
+++ b/arch/s390/pci/Makefile
@@ -5,6 +5,6 @@

obj-$(CONFIG_PCI) += pci.o pci_irq.o pci_clp.o \
pci_event.o pci_debug.o pci_insn.o pci_mmio.o \
- pci_bus.o pci_kvm_hook.o pci_report.o
+ pci_bus.o pci_kvm_hook.o pci_report.o pci_fixup.o
obj-$(CONFIG_PCI_IOV) += pci_iov.o
obj-$(CONFIG_SYSFS) += pci_sysfs.o
diff --git a/arch/s390/pci/pci_fixup.c b/arch/s390/pci/pci_fixup.c
new file mode 100644
index 0000000000000000000000000000000000000000..35688b645098329f082d0c40cc8c59231c390eaa
--- /dev/null
+++ b/arch/s390/pci/pci_fixup.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Exceptions for specific devices,
+ *
+ * Copyright IBM Corp. 2025
+ *
+ * Author(s):
+ * Niklas Schnelle <schnelle@linux.ibm.com>
+ */
+#include <linux/pci.h>
+
+static void zpci_ism_bar_no_mmap(struct pci_dev *pdev)
+{
+ /*
+ * ISM's BAR is special. Drivers written for ISM know
+ * how to handle this but others need to be aware of their
+ * special nature e.g. to prevent attempts to mmap() it.
+ */
+ pdev->non_mappable_bars = 1;
+}
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_IBM,
+ PCI_DEVICE_ID_IBM_ISM,
+ zpci_ism_bar_no_mmap);
diff --git a/drivers/s390/net/ism_drv.c b/drivers/s390/net/ism_drv.c
index e36e3ea165d3b2b01d68e53634676cb8c2c40220..d32633ed9fa80c1764724f493b363bfd6cb4f9cf 100644
--- a/drivers/s390/net/ism_drv.c
+++ b/drivers/s390/net/ism_drv.c
@@ -20,7 +20,6 @@
MODULE_DESCRIPTION("ISM driver for s390");
MODULE_LICENSE("GPL");

-#define PCI_DEVICE_ID_IBM_ISM 0x04ED
#define DRV_NAME "ism"

static const struct pci_device_id ism_device_table[] = {
diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index bf50ffa10bdea9e52a9d01cc3d6ee4cade39a08c..c3bcb6911c538286f7985f9c5e938d587fc04b56 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -7,10 +7,6 @@ config VFIO_PCI_CORE
select VFIO_VIRQFD
select IRQ_BYPASS_MANAGER

-config VFIO_PCI_MMAP
- def_bool y if !S390
- depends on VFIO_PCI_CORE
-
config VFIO_PCI_INTX
def_bool y if !S390
depends on VFIO_PCI_CORE
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 586e49efb81be32ccb50ca554a60cec684c37402..c8586d47704c74cf9a5256d65bbf888db72b2f91 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -116,7 +116,7 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device *vdev)

res = &vdev->pdev->resource[bar];

- if (!IS_ENABLED(CONFIG_VFIO_PCI_MMAP))
+ if (vdev->pdev->non_mappable_bars)
goto no_mmap;

if (!(res->flags & IORESOURCE_MEM))
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 47b31ad724fa5bf7abd7c3dc572947551b0f2148..7192b9d78d7e337ce6144190325458fe3c0f1696 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -476,6 +476,7 @@ struct pci_dev {
unsigned int no_command_memory:1; /* No PCI_COMMAND_MEMORY */
unsigned int rom_bar_overlap:1; /* ROM BAR disable broken */
unsigned int rom_attr_enabled:1; /* Display of ROM attribute enabled? */
+ unsigned int non_mappable_bars:1; /* BARs can't be mapped to user-space */
pci_dev_flags_t dev_flags;
atomic_t enable_cnt; /* pci_enable_device has been called */

diff --git a/include/linux/pci_ids.h b/include/linux/pci_ids.h
index de5deb1a0118fcf56570d461cbe7a501d4bd0da3..ec6d311ed12e174dc0bad2ce8c92454bed668fee 100644
--- a/include/linux/pci_ids.h
+++ 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

#define PCI_SUBVENDOR_ID_IBM 0x1014
#define PCI_SUBDEVICE_ID_IBM_SATURN_SERIAL_ONE_PORT 0x03d4

--
2.45.2