6.6-stable review patch. If anyone has any objections, please let me know.
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From: Shin'ichiro Kawasaki shinichiro.kawasaki@wdc.com
commit b28ff7a7c3245d7f62acc20f15b4361292fe4117 upstream.
p2sb_bar() unhides P2SB device to get resources from the device. It guards the operation by locking pci_rescan_remove_lock so that parallel rescans do not find the P2SB device. However, this lock causes deadlock when PCI bus rescan is triggered by /sys/bus/pci/rescan. The rescan locks pci_rescan_remove_lock and probes PCI devices. When PCI devices call p2sb_bar() during probe, it locks pci_rescan_remove_lock again. Hence the deadlock.
To avoid the deadlock, do not lock pci_rescan_remove_lock in p2sb_bar(). Instead, do the lock at fs_initcall. Introduce p2sb_cache_resources() for fs_initcall which gets and caches the P2SB resources. At p2sb_bar(), refer the cache and return to the caller.
Suggested-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Fixes: 9745fb07474f ("platform/x86/intel: Add Primary to Sideband (P2SB) bridge support") Cc: stable@vger.kernel.org Signed-off-by: Shin'ichiro Kawasaki shinichiro.kawasaki@wdc.com Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Reviewed-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Link: https://lore.kernel.org/linux-pci/6xb24fjmptxxn5js2fjrrddjae6twex5bjaftwqsua... Link: https://lore.kernel.org/r/20231229063912.2517922-2-shinichiro.kawasaki@wdc.c... Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/platform/x86/p2sb.c | 172 +++++++++++++++++++++++++++++++++----------- 1 file changed, 131 insertions(+), 41 deletions(-)
--- a/drivers/platform/x86/p2sb.c +++ b/drivers/platform/x86/p2sb.c @@ -26,6 +26,21 @@ static const struct x86_cpu_id p2sb_cpu_ {} };
+/* + * Cache BAR0 of P2SB device functions 0 to 7. + * TODO: The constant 8 is the number of functions that PCI specification + * defines. Same definitions exist tree-wide. Unify this definition and + * the other definitions then move to include/uapi/linux/pci.h. + */ +#define NR_P2SB_RES_CACHE 8 + +struct p2sb_res_cache { + u32 bus_dev_id; + struct resource res; +}; + +static struct p2sb_res_cache p2sb_resources[NR_P2SB_RES_CACHE]; + static int p2sb_get_devfn(unsigned int *devfn) { unsigned int fn = P2SB_DEVFN_DEFAULT; @@ -39,8 +54,16 @@ static int p2sb_get_devfn(unsigned int * return 0; }
+static bool p2sb_valid_resource(struct resource *res) +{ + if (res->flags) + return true; + + return false; +} + /* Copy resource from the first BAR of the device in question */ -static int p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem) +static void p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem) { struct resource *bar0 = &pdev->resource[0];
@@ -56,47 +79,64 @@ static int p2sb_read_bar0(struct pci_dev mem->end = bar0->end; mem->flags = bar0->flags; mem->desc = bar0->desc; - - return 0; }
-static int p2sb_scan_and_read(struct pci_bus *bus, unsigned int devfn, struct resource *mem) +static void p2sb_scan_and_cache_devfn(struct pci_bus *bus, unsigned int devfn) { + struct p2sb_res_cache *cache = &p2sb_resources[PCI_FUNC(devfn)]; struct pci_dev *pdev; - int ret;
pdev = pci_scan_single_device(bus, devfn); if (!pdev) - return -ENODEV; + return;
- ret = p2sb_read_bar0(pdev, mem); + p2sb_read_bar0(pdev, &cache->res); + cache->bus_dev_id = bus->dev.id;
pci_stop_and_remove_bus_device(pdev); - return ret; + return; }
-/** - * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR - * @bus: PCI bus to communicate with - * @devfn: PCI slot and function to communicate with - * @mem: memory resource to be filled in - * - * The BIOS prevents the P2SB device from being enumerated by the PCI - * subsystem, so we need to unhide and hide it back to lookup the BAR. - * - * if @bus is NULL, the bus 0 in domain 0 will be used. - * If @devfn is 0, it will be replaced by devfn of the P2SB device. - * - * Caller must provide a valid pointer to @mem. - * - * Locking is handled by pci_rescan_remove_lock mutex. - * - * Return: - * 0 on success or appropriate errno value on error. - */ -int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) +static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn) { - struct pci_dev *pdev_p2sb; + unsigned int slot, fn; + + if (PCI_FUNC(devfn) == 0) { + /* + * When function number of the P2SB device is zero, scan it and + * other function numbers, and if devices are available, cache + * their BAR0s. + */ + slot = PCI_SLOT(devfn); + for (fn = 0; fn < NR_P2SB_RES_CACHE; fn++) + p2sb_scan_and_cache_devfn(bus, PCI_DEVFN(slot, fn)); + } else { + /* Scan the P2SB device and cache its BAR0 */ + p2sb_scan_and_cache_devfn(bus, devfn); + } + + if (!p2sb_valid_resource(&p2sb_resources[PCI_FUNC(devfn)].res)) + return -ENOENT; + + return 0; +} + +static struct pci_bus *p2sb_get_bus(struct pci_bus *bus) +{ + static struct pci_bus *p2sb_bus; + + bus = bus ?: p2sb_bus; + if (bus) + return bus; + + /* Assume P2SB is on the bus 0 in domain 0 */ + p2sb_bus = pci_find_bus(0, 0); + return p2sb_bus; +} + +static int p2sb_cache_resources(void) +{ + struct pci_bus *bus; unsigned int devfn_p2sb; u32 value = P2SBC_HIDE; int ret; @@ -106,8 +146,9 @@ int p2sb_bar(struct pci_bus *bus, unsign if (ret) return ret;
- /* if @bus is NULL, use bus 0 in domain 0 */ - bus = bus ?: pci_find_bus(0, 0); + bus = p2sb_get_bus(NULL); + if (!bus) + return -ENODEV;
/* * Prevent concurrent PCI bus scan from seeing the P2SB device and @@ -115,17 +156,16 @@ int p2sb_bar(struct pci_bus *bus, unsign */ pci_lock_rescan_remove();
- /* Unhide the P2SB device, if needed */ + /* + * The BIOS prevents the P2SB device from being enumerated by the PCI + * subsystem, so we need to unhide and hide it back to lookup the BAR. + * Unhide the P2SB device here, if needed. + */ pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value); if (value & P2SBC_HIDE) pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, 0);
- pdev_p2sb = pci_scan_single_device(bus, devfn_p2sb); - if (devfn) - ret = p2sb_scan_and_read(bus, devfn, mem); - else - ret = p2sb_read_bar0(pdev_p2sb, mem); - pci_stop_and_remove_bus_device(pdev_p2sb); + ret = p2sb_scan_and_cache(bus, devfn_p2sb);
/* Hide the P2SB device, if it was hidden */ if (value & P2SBC_HIDE) @@ -133,12 +173,62 @@ int p2sb_bar(struct pci_bus *bus, unsign
pci_unlock_rescan_remove();
- if (ret) - return ret; + return ret; +}
- if (mem->flags == 0) +/** + * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR + * @bus: PCI bus to communicate with + * @devfn: PCI slot and function to communicate with + * @mem: memory resource to be filled in + * + * If @bus is NULL, the bus 0 in domain 0 will be used. + * If @devfn is 0, it will be replaced by devfn of the P2SB device. + * + * Caller must provide a valid pointer to @mem. + * + * Return: + * 0 on success or appropriate errno value on error. + */ +int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) +{ + struct p2sb_res_cache *cache; + int ret; + + bus = p2sb_get_bus(bus); + if (!bus) + return -ENODEV; + + if (!devfn) { + ret = p2sb_get_devfn(&devfn); + if (ret) + return ret; + } + + cache = &p2sb_resources[PCI_FUNC(devfn)]; + if (cache->bus_dev_id != bus->dev.id) return -ENODEV;
+ if (!p2sb_valid_resource(&cache->res)) + return -ENOENT; + + memcpy(mem, &cache->res, sizeof(*mem)); return 0; } EXPORT_SYMBOL_GPL(p2sb_bar); + +static int __init p2sb_fs_init(void) +{ + p2sb_cache_resources(); + return 0; +} + +/* + * pci_rescan_remove_lock to avoid access to unhidden P2SB devices can + * not be locked in sysfs pci bus rescan path because of deadlock. To + * avoid the deadlock, access to P2SB devices with the lock at an early + * step in kernel initialization and cache required resources. This + * should happen after subsys_initcall which initializes PCI subsystem + * and before device_initcall which requires P2SB resources. + */ +fs_initcall(p2sb_fs_init);