Unverified Commit b28ff7a7 authored by Shin'ichiro Kawasaki's avatar Shin'ichiro Kawasaki Committed by Ilpo Järvinen
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platform/x86: p2sb: Allow p2sb_bar() calls during PCI device probe 



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: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Fixes: 9745fb07 ("platform/x86/intel: Add Primary to Sideband (P2SB) bridge support")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarShin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/linux-pci/6xb24fjmptxxn5js2fjrrddjae6twex5bjaftwqsuawuqqqydx@7cl3uik5ef6j/
Link: https://lore.kernel.org/r/20231229063912.2517922-2-shinichiro.kawasaki@wdc.com


Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
parent a55bdad5

drivers/platform/x86/p2sb.c

+131 −41
Original line number Diff line number Diff line
@@ -26,6 +26,21 @@ static const struct x86_cpu_id p2sb_cpu_ids[] = { 
	{}

};



/*

 * 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 *devfn) 
	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 *pdev, struct resource *mem) 
	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.

static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn)

{

	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.

		 */

int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)

		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)

{

	struct pci_dev *pdev_p2sb;

	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, unsigned int devfn, struct resource *mem) 
	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, unsigned int devfn, struct resource *mem) 
	 */

	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, unsigned int devfn, struct resource *mem) 


	pci_unlock_rescan_remove();



	return ret;

}



/**

 * 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;

	}



	if (mem->flags == 0)

	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);