[PATCH 4.9 16/43] PCI/MSI: Mask all unused MSI-X entries

From: Sasha Levin
Date: Tue Aug 24 2021 - 13:36:51 EST

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit 7d5ec3d3612396dc6d4b76366d20ab9fc06f399f upstream.

When MSI-X is enabled the ordering of calls is:


This has a few interesting issues:

1) msix_setup_entries() allocates the MSI descriptors and initializes them
except for the msi_desc:masked member which is left zero initialized.

2) pci_msi_setup_msi_irqs() allocates the interrupt descriptors and sets
up the MSI interrupts which ends up in pci_write_msi_msg() unless the
interrupt chip provides its own irq_write_msi_msg() function.

3) msix_program_entries() does not do what the name suggests. It solely
updates the entries array (if not NULL) and initializes the masked
member for each MSI descriptor by reading the hardware state and then
masks the entry.

Obviously this has some issues:

1) The uninitialized masked member of msi_desc prevents the enforcement
of masking the entry in pci_write_msi_msg() depending on the cached
masked bit. Aside of that half initialized data is a NONO in general

2) msix_program_entries() only ensures that the actually allocated entries
are masked. This is wrong as experimentation with crash testing and
crash kernel kexec has shown.

This limited testing unearthed that when the production kernel had more
entries in use and unmasked when it crashed and the crash kernel
allocated a smaller amount of entries, then a full scan of all entries
found unmasked entries which were in use in the production kernel.

This is obviously a device or emulation issue as the device reset
should mask all MSI-X table entries, but obviously that's just part
of the paper specification.

Cure this by:

1) Masking all table entries in hardware
2) Initializing msi_desc::masked in msix_setup_entries()
3) Removing the mask dance in msix_program_entries()
4) Renaming msix_program_entries() to msix_update_entries() to
reflect the purpose of that function.

As the masking of unused entries has never been done the Fixes tag refers
to a commit in:

Fixes: f036d4ea5fa7 ("[PATCH] ia32 Message Signalled Interrupt support")
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Marc Zyngier <maz@xxxxxxxxxx>
Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20210729222542.403833459@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/pci/msi.c | 39 ++++++++++++++++++++++++++++-----------
1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 79b36f1bde0d..a4873c7fea72 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -695,6 +695,7 @@ static int msix_setup_entries(struct pci_dev *dev, void __iomem *base,
struct cpumask *curmsk, *masks = NULL;
struct msi_desc *entry;
+ void __iomem *addr;
int ret, i;

if (affinity) {
@@ -717,6 +718,7 @@ static int msix_setup_entries(struct pci_dev *dev, void __iomem *base,

entry->msi_attrib.is_msix = 1;
entry->msi_attrib.is_64 = 1;
if (entries)
entry->msi_attrib.entry_nr = entries[i].entry;
@@ -724,6 +726,10 @@ static int msix_setup_entries(struct pci_dev *dev, void __iomem *base,
entry->msi_attrib.default_irq = dev->irq;
entry->mask_base = base;

+ addr = pci_msix_desc_addr(entry);
+ if (addr)
+ entry->masked = readl(addr + PCI_MSIX_ENTRY_VECTOR_CTRL);
list_add_tail(&entry->list, dev_to_msi_list(&dev->dev));
if (masks)
@@ -734,21 +740,27 @@ out:
return ret;

-static void msix_program_entries(struct pci_dev *dev,
- struct msix_entry *entries)
+static void msix_update_entries(struct pci_dev *dev, struct msix_entry *entries)
struct msi_desc *entry;
- int i = 0;

for_each_pci_msi_entry(entry, dev) {
- if (entries)
- entries[i++].vector = entry->irq;
- entry->masked = readl(pci_msix_desc_addr(entry) +
- msix_mask_irq(entry, 1);
+ if (entries) {
+ entries->vector = entry->irq;
+ entries++;
+ }

+static void msix_mask_all(void __iomem *base, int tsize)
+ int i;
+ for (i = 0; i < tsize; i++, base += PCI_MSIX_ENTRY_SIZE)
+ writel(ctrl, base + PCI_MSIX_ENTRY_VECTOR_CTRL);
* msix_capability_init - configure device's MSI-X capability
* @dev: pointer to the pci_dev data structure of MSI-X device function
@@ -763,9 +775,9 @@ static void msix_program_entries(struct pci_dev *dev,
static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
int nvec, bool affinity)
- int ret;
- u16 control;
void __iomem *base;
+ int ret, tsize;
+ u16 control;

* Some devices require MSI-X to be enabled before the MSI-X
@@ -777,12 +789,17 @@ static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,

pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &control);
/* Request & Map MSI-X table region */
+ tsize = msix_table_size(control);
+ base = msix_map_region(dev, tsize);
base = msix_map_region(dev, msix_table_size(control));
if (!base) {
ret = -ENOMEM;
goto out_disable;

+ /* Ensure that all table entries are masked. */
+ msix_mask_all(base, tsize);
ret = msix_setup_entries(dev, base, entries, nvec, affinity);
if (ret)
goto out_disable;
@@ -796,7 +813,7 @@ static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
if (ret)
goto out_free;

- msix_program_entries(dev, entries);
+ msix_update_entries(dev, entries);

ret = populate_msi_sysfs(dev);
if (ret)