PCI: Add locking to RMW PCI Express Capability Register accessors

Many places in the kernel write the Link Control and Root Control PCI
Express Capability Registers without proper concurrency control and this
could result in losing the changes one of the writers intended to make.

Add pcie_cap_lock spinlock into the struct pci_dev and use it to protect
bit changes made in the RMW capability accessors. Protect only a selected
set of registers by differentiating the RMW accessor internally to
locked/unlocked variants using a wrapper which has the same signature as
pcie_capability_clear_and_set_word(). As the Capability Register (pos)
given to the wrapper is always a constant, the compiler should be able to
simplify all the dead-code away.

So far only the Link Control Register (ASPM, hotplug, link retraining,
various drivers) and the Root Control Register (AER & PME) seem to
require RMW locking.

Suggested-by: Lukas Wunner <lukas@wunner.de>
Fixes: c7f4865 ("PCI PM: PCIe PME root port service driver")
Fixes: f12eb72 ("PCI/ASPM: Use PCI Express Capability accessors")
Fixes: 7d715a6 ("PCI: add PCI Express ASPM support")
Fixes: affa48d ("staging/rdma/hfi1: Add support for enabling/disabling PCIe ASPM")
Fixes: 849a936 ("misc: rtsx: Add support new chip rts5228 mmc: rtsx: Add support MMC_CAP2_NO_MMC")
Fixes: 3d1e7aa ("misc: rtsx: Use pcie_capability_clear_and_set_word() for PCI_EXP_LNKCTL")
Fixes: c0e5f4e ("misc: rtsx: Add support for RTS5261")
Fixes: 3df4fce ("misc: rtsx: separate aspm mode into MODE_REG and MODE_CFG")
Fixes: 121e9c6 ("misc: rtsx: modify and fix init_hw function")
Fixes: 19f3bd5 ("mfd: rtsx: Remove LCTLR defination")
Fixes: 773ccdf ("mfd: rtsx: Read vendor setting from config space")
Fixes: 8275b77 ("mfd: rts5249: Add support for RTS5250S power saving")
Fixes: 5da4e04 ("misc: rtsx: Add support for RTS5260")
Fixes: 0f49bfb ("tg3: Use PCI Express Capability accessors")
Fixes: 5e7dfd0 ("tg3: Prevent corruption at 10 / 100Mbps w CLKREQ")
Fixes: b726e49 ("r8169: sync existing 8168 device hardware start sequences with vendor driver")
Fixes: e6de30d ("r8169: more 8168dp support.")
Fixes: 8a06127 ("Bluetooth: hci_bcm4377: Add new driver for BCM4377 PCIe boards")
Fixes: 6f461f6 ("e1000e: enable/disable ASPM L0s and L1 and ERT according to hardware errata")
Fixes: 1eae4eb ("e1000e: Disable L1 ASPM power savings for 82573 mobile variants")
Fixes: 8060e16 ("ath9k: Enable extended synch for AR9485 to fix L0s recovery issue")
Fixes: 69ce674 ("ath9k: do btcoex ASPM disabling at initialization time")
Fixes: f37f055 ("mt76: mt76x2e: disable pcie_aspm by default")
Link: https://lore.kernel.org/r/20230717120503.15276-2-ilpo.jarvinen@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: "Rafael J. Wysocki" <rafael@kernel.org>

Author: ij-intel

drivers/pci/access.c

@@ -497,8 +497,8 @@ int pcie_capability_write_dword(struct pci_dev *dev, int pos, u32 val)
 }
 EXPORT_SYMBOL(pcie_capability_write_dword);
 
-int pcie_capability_clear_and_set_word(struct pci_dev *dev, int pos,
-				       u16 clear, u16 set)
+int pcie_capability_clear_and_set_word_unlocked(struct pci_dev *dev, int pos,
+						u16 clear, u16 set)
 {
 	int ret;
 	u16 val;
@@ -512,7 +512,21 @@ int pcie_capability_clear_and_set_word(struct pci_dev *dev, int pos,
 
 	return ret;
 }
-EXPORT_SYMBOL(pcie_capability_clear_and_set_word);
+EXPORT_SYMBOL(pcie_capability_clear_and_set_word_unlocked);
+
+int pcie_capability_clear_and_set_word_locked(struct pci_dev *dev, int pos,
+					      u16 clear, u16 set)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&dev->pcie_cap_lock, flags);
+	ret = pcie_capability_clear_and_set_word_unlocked(dev, pos, clear, set);
+	spin_unlock_irqrestore(&dev->pcie_cap_lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL(pcie_capability_clear_and_set_word_locked);
 
 int pcie_capability_clear_and_set_dword(struct pci_dev *dev, int pos,
 					u32 clear, u32 set)

drivers/pci/probe.c

@@ -2324,6 +2324,7 @@ struct pci_dev *pci_alloc_dev(struct pci_bus *bus)
 		.end = -1,
 	};
 
+	spin_lock_init(&dev->pcie_cap_lock);
 #ifdef CONFIG_PCI_MSI
 	raw_spin_lock_init(&dev->msi_lock);
 #endif

include/linux/pci.h

@@ -467,6 +467,7 @@ struct pci_dev {
 	pci_dev_flags_t dev_flags;
 	atomic_t	enable_cnt;	/* pci_enable_device has been called */
 
+	spinlock_t	pcie_cap_lock;		/* Protects RMW ops in capability accessors */
 	u32		saved_config_space[16]; /* Config space saved at suspend time */
 	struct hlist_head saved_cap_space;
 	int		rom_attr_enabled;	/* Display of ROM attribute enabled? */
@@ -1217,11 +1218,40 @@ int pcie_capability_read_word(struct pci_dev *dev, int pos, u16 *val);
 int pcie_capability_read_dword(struct pci_dev *dev, int pos, u32 *val);
 int pcie_capability_write_word(struct pci_dev *dev, int pos, u16 val);
 int pcie_capability_write_dword(struct pci_dev *dev, int pos, u32 val);
-int pcie_capability_clear_and_set_word(struct pci_dev *dev, int pos,
-				       u16 clear, u16 set);
+int pcie_capability_clear_and_set_word_unlocked(struct pci_dev *dev, int pos,
+						u16 clear, u16 set);
+int pcie_capability_clear_and_set_word_locked(struct pci_dev *dev, int pos,
+					      u16 clear, u16 set);
 int pcie_capability_clear_and_set_dword(struct pci_dev *dev, int pos,
 					u32 clear, u32 set);
 
+/**
+ * pcie_capability_clear_and_set_word - RMW accessor for PCI Express Capability Registers
+ * @dev:	PCI device structure of the PCI Express device
+ * @pos:	PCI Express Capability Register
+ * @clear:	Clear bitmask
+ * @set:	Set bitmask
+ *
+ * Perform a Read-Modify-Write (RMW) operation using @clear and @set
+ * bitmasks on PCI Express Capability Register at @pos. Certain PCI Express
+ * Capability Registers are accessed concurrently in RMW fashion, hence
+ * require locking which is handled transparently to the caller.
+ */
+static inline int pcie_capability_clear_and_set_word(struct pci_dev *dev,
+						     int pos,
+						     u16 clear, u16 set)
+{
+	switch (pos) {
+	case PCI_EXP_LNKCTL:
+	case PCI_EXP_RTCTL:
+		return pcie_capability_clear_and_set_word_locked(dev, pos,
+								 clear, set);
+	default:
+		return pcie_capability_clear_and_set_word_unlocked(dev, pos,
+								   clear, set);
+	}
+}
+
 static inline int pcie_capability_set_word(struct pci_dev *dev, int pos,
 					   u16 set)
 {