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    Subject[PATCH 5.10 79/96] PCI/MSI: Enable and mask MSI-X early
    Date
    From: Thomas Gleixner <tglx@linutronix.de>

    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 d71d6432e105 ("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: d71d6432e105 ("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>
    ---
    drivers/pci/msi.c | 28 +++++++++++++++-------------
    1 file changed, 15 insertions(+), 13 deletions(-)

    --- a/drivers/pci/msi.c
    +++ b/drivers/pci/msi.c
    @@ -779,18 +779,25 @@ static int msix_capability_init(struct p
    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)
    @@ -801,14 +808,6 @@ static int msix_capability_init(struct p
    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);
    @@ -843,6 +842,9 @@ out_avail:
    out_free:
    free_msi_irqs(dev);

    +out_disable:
    + pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_ENABLE, 0);
    +
    return ret;
    }


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