[PATCH 1/6] PCI/ASPM: Add locked helper for enabling link state

Johan Hovold
2023-11-14T13:56:51Z

Add a helper for enabling link states that can be used in contexts where
a pci_bus_sem read lock is already held (e.g. from pci_walk_bus()).

This helper will be used to fix a couple of potential deadlocks where
the current helper is called with the lock already held, hence the CC
stable tag.

Fixes: f492edb40b54 ("PCI: vmd: Add quirk to configure PCIe ASPM and LTR")
Cc: stable@vger.kernel.org # 6.3
Cc: Michael Bottini <michael.a.bottini@linux.intel.com>
Cc: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
drivers/pci/pcie/aspm.c | 53 +++++++++++++++++++++++++++++++----------
include/linux/pci.h | 3 +++
2 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 50b04ae5c394..8cf8cc2d6bba 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -1109,17 +1109,7 @@ int pci_disable_link_state(struct pci_dev *pdev, int state)
}
EXPORT_SYMBOL(pci_disable_link_state);

-/**
- * pci_enable_link_state - Clear and set the default device link state so that
- * the link may be allowed to enter the specified states. Note that if the
- * BIOS didn't grant ASPM control to the OS, this does nothing because we can't
- * touch the LNKCTL register. Also note that this does not enable states
- * disabled by pci_disable_link_state(). Return 0 or a negative errno.
- *
- * @pdev: PCI device
- * @state: Mask of ASPM link states to enable
- */
-int pci_enable_link_state(struct pci_dev *pdev, int state)
+static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
{
struct pcie_link_state *link = pcie_aspm_get_link(pdev);

@@ -1136,7 +1126,8 @@ int pci_enable_link_state(struct pci_dev *pdev, int state)
return -EPERM;
}

- down_read(&pci_bus_sem);
+ if (!locked)
+ down_read(&pci_bus_sem);
mutex_lock(&aspm_lock);
link->aspm_default = 0;
if (state & PCIE_LINK_STATE_L0S)
@@ -1157,12 +1148,48 @@ int pci_enable_link_state(struct pci_dev *pdev, int state)
link->clkpm_default = (state & PCIE_LINK_STATE_CLKPM) ? 1 : 0;
pcie_set_clkpm(link, policy_to_clkpm_state(link));
mutex_unlock(&aspm_lock);
- up_read(&pci_bus_sem);
+ if (!locked)
+ up_read(&pci_bus_sem);

return 0;
}
+
+/**
+ * pci_enable_link_state - Clear and set the default device link state so that
+ * the link may be allowed to enter the specified states. Note that if the
+ * BIOS didn't grant ASPM control to the OS, this does nothing because we can't
+ * touch the LNKCTL register. Also note that this does not enable states
+ * disabled by pci_disable_link_state(). Return 0 or a negative errno.
+ *
+ * @pdev: PCI device
+ * @state: Mask of ASPM link states to enable
+ */
+int pci_enable_link_state(struct pci_dev *pdev, int state)
+{
+ return __pci_enable_link_state(pdev, state, false);
+}
EXPORT_SYMBOL(pci_enable_link_state);

+/**
+ * pci_enable_link_state - Clear and set the default device link state so that
+ * the link may be allowed to enter the specified states. Note that if the
+ * BIOS didn't grant ASPM control to the OS, this does nothing because we can't
+ * touch the LNKCTL register. Also note that this does not enable states
+ * disabled by pci_disable_link_state(). Return 0 or a negative errno.
+ *
+ * @pdev: PCI device
+ * @state: Mask of ASPM link states to enable
+ *
+ * Context: Caller holds pci_bus_sem read lock.
+ */
+int pci_enable_link_state_locked(struct pci_dev *pdev, int state)
+{
+ lockdep_assert_held_read(&pci_bus_sem);
+
+ return __pci_enable_link_state(pdev, state, true);
+}
+EXPORT_SYMBOL(pci_enable_link_state_locked);
+
static int pcie_aspm_set_policy(const char *val,
const struct kernel_param *kp)
{
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 60ca768bc867..dea043bc1e38 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1829,6 +1829,7 @@ extern bool pcie_ports_native;
int pci_disable_link_state(struct pci_dev *pdev, int state);
int pci_disable_link_state_locked(struct pci_dev *pdev, int state);
int pci_enable_link_state(struct pci_dev *pdev, int state);
+int pci_enable_link_state_locked(struct pci_dev *pdev, int state);
void pcie_no_aspm(void);
bool pcie_aspm_support_enabled(void);
bool pcie_aspm_enabled(struct pci_dev *pdev);
@@ -1839,6 +1840,8 @@ static inline int pci_disable_link_state_locked(struct pci_dev *pdev, int state)
{ return 0; }
static inline int pci_enable_link_state(struct pci_dev *pdev, int state)
{ return 0; }
+static inline int pci_enable_link_state_locked(struct pci_dev *pdev, int state)
+{ return 0; }
static inline void pcie_no_aspm(void) { }
static inline bool pcie_aspm_support_enabled(void) { return false; }
static inline bool pcie_aspm_enabled(struct pci_dev *pdev) { return false; }
--
2.41.0