Commit 3b4220c2 authored Jul 29, 2021 by Thomas Gleixner Committed by Greg Kroah-Hartman Aug 18, 2021

PCI/MSI: Enable and mask MSI-X early



commit 438553958ba19296663c6d6583d208dfb6792830 upstream.

The ordering of MSI-X enable in hardware is dysfunctional:

 1) MSI-X is disabled in the control register
 2) Various setup functions
 3) pci_msi_setup_msi_irqs() is invoked which ends up accessing
    the MSI-X table entries
 4) MSI-X is enabled and masked in the control register with the
    comment that enabling is required for some hardware to access
    the MSI-X table

Step #4 obviously contradicts #3. The history of this is an issue with the
NIU hardware. When #4 was introduced the table access actually happened in
msix_program_entries() which was invoked after enabling and masking MSI-X.

This was changed in commit d71d6432 ("PCI/MSI: Kill redundant call of
irq_set_msi_desc() for MSI-X interrupts") which removed the table write
from msix_program_entries().

Interestingly enough nobody noticed and either NIU still works or it did
not get any testing with a kernel 3.19 or later.

Nevertheless this is inconsistent and there is no reason why MSI-X can't be
enabled and masked in the control register early on, i.e. move step #4
above to step #1. This preserves the NIU workaround and has no side effects
on other hardware.

Fixes: d71d6432 ("PCI/MSI: Kill redundant call of irq_set_msi_desc() for MSI-X interrupts")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210729222542.344136412@linutronix.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 0c8dea3f

drivers/pci/msi.c

+15 −13

Original line number	Diff line number	Diff line
		@@ -778,18 +778,25 @@ static int msix_capability_init(struct pci_dev dev, struct msix_entry entries,
		u16 control;
		void __iomem *base;

		/* Ensure MSI-X is disabled while it is set up */
		pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_ENABLE, 0);
		/*
		* Some devices require MSI-X to be enabled before the MSI-X
		* registers can be accessed. Mask all the vectors to prevent
		* interrupts coming in before they're fully set up.
		*/
		pci_msix_clear_and_set_ctrl(dev, 0, PCI_MSIX_FLAGS_MASKALL \|
		PCI_MSIX_FLAGS_ENABLE);

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

		ret = msix_setup_entries(dev, base, entries, nvec, affd);
		if (ret)
		return ret;
		goto out_disable;

		ret = pci_msi_setup_msi_irqs(dev, nvec, PCI_CAP_ID_MSIX);
		if (ret)
		@@ -800,14 +807,6 @@ static int msix_capability_init(struct pci_dev dev, struct msix_entry entries,
		if (ret)
		goto out_free;

		/*
		* Some devices require MSI-X to be enabled before we can touch the
		* MSI-X registers. We need to mask all the vectors to prevent
		* interrupts coming in before they're fully set up.
		*/
		pci_msix_clear_and_set_ctrl(dev, 0,
		PCI_MSIX_FLAGS_MASKALL \| PCI_MSIX_FLAGS_ENABLE);

		msix_program_entries(dev, entries);

		ret = populate_msi_sysfs(dev);
		@@ -842,6 +841,9 @@ static int msix_capability_init(struct pci_dev dev, struct msix_entry entries,
		out_free:
		free_msi_irqs(dev);

		out_disable:
		pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_ENABLE, 0);

		return ret;
		}