[PATCH 4.9 15/43] PCI/MSI: Protect msi_desc::masked for multi-MSI

From: Sasha Levin
Date: Tue Aug 24 2021 - 13:36:52 EST

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit 77e89afc25f30abd56e76a809ee2884d7c1b63ce upstream.

Multi-MSI uses a single MSI descriptor and there is a single mask register
when the device supports per vector masking. To avoid reading back the mask
register the value is cached in the MSI descriptor and updates are done by
clearing and setting bits in the cache and writing it to the device.

But nothing protects msi_desc::masked and the mask register from being
modified concurrently on two different CPUs for two different Linux
interrupts which belong to the same multi-MSI descriptor.

Add a lock to struct device and protect any operation on the mask and the
mask register with it.

This makes the update of msi_desc::masked unconditional, but there is no
place which requires a modification of the hardware register without
updating the masked cache.

msi_mask_irq() is now an empty wrapper which will be cleaned up in follow
up changes.

The problem goes way back to the initial support of multi-MSI, but picking
the commit which introduced the mask cache is a valid cut off point

Fixes: f2440d9acbe8 ("PCI MSI: Refactor interrupt masking code")
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Marc Zyngier <maz@xxxxxxxxxx>
Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20210729222542.726833414@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/base/core.c | 1 +
drivers/pci/msi.c | 19 ++++++++++---------
include/linux/device.h | 1 +
include/linux/msi.h | 2 +-
4 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 3b8487e28c84..e82a89325f3d 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -710,6 +710,7 @@ void device_initialize(struct device *dev)
set_dev_node(dev, -1);
+ raw_spin_lock_init(&dev->msi_lock);
diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index b3977b4c51b6..79b36f1bde0d 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -189,24 +189,25 @@ static inline __attribute_const__ u32 msi_mask(unsigned x)
* reliably as devices without an INTx disable bit will then generate a
* level IRQ which will never be cleared.
-u32 __pci_msi_desc_mask_irq(struct msi_desc *desc, u32 mask, u32 flag)
+void __pci_msi_desc_mask_irq(struct msi_desc *desc, u32 mask, u32 flag)
- u32 mask_bits = desc->masked;
+ raw_spinlock_t *lock = &desc->dev->msi_lock;
+ unsigned long flags;

if (pci_msi_ignore_mask || !desc->msi_attrib.maskbit)
- return 0;
+ return;

- mask_bits &= ~mask;
- mask_bits |= flag;
+ raw_spin_lock_irqsave(lock, flags);
+ desc->masked &= ~mask;
+ desc->masked |= flag;
pci_write_config_dword(msi_desc_to_pci_dev(desc), desc->mask_pos,
- mask_bits);
- return mask_bits;
+ desc->masked);
+ raw_spin_unlock_irqrestore(lock, flags);

static void msi_mask_irq(struct msi_desc *desc, u32 mask, u32 flag)
- desc->masked = __pci_msi_desc_mask_irq(desc, mask, flag);
+ __pci_msi_desc_mask_irq(desc, mask, flag);

static void __iomem *pci_msix_desc_addr(struct msi_desc *desc)
diff --git a/include/linux/device.h b/include/linux/device.h
index eb865b461acc..ca765188a981 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -812,6 +812,7 @@ struct device {
struct dev_pin_info *pins;
+ raw_spinlock_t msi_lock;
struct list_head msi_list;

diff --git a/include/linux/msi.h b/include/linux/msi.h
index debc8aa4ec19..601bff9fbbec 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -133,7 +133,7 @@ void __pci_write_msi_msg(struct msi_desc *entry, struct msi_msg *msg);
void pci_write_msi_msg(unsigned int irq, struct msi_msg *msg);

u32 __pci_msix_desc_mask_irq(struct msi_desc *desc, u32 flag);
-u32 __pci_msi_desc_mask_irq(struct msi_desc *desc, u32 mask, u32 flag);
+void __pci_msi_desc_mask_irq(struct msi_desc *desc, u32 mask, u32 flag);
void pci_msi_mask_irq(struct irq_data *data);
void pci_msi_unmask_irq(struct irq_data *data);