Patch "xen-pciback: Consider INTx disabled when MSI/MSI-X is enabled" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    xen-pciback: Consider INTx disabled when MSI/MSI-X is enabled

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     xen-pciback-consider-intx-disabled-when-msi-msi-x-is.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit caba343a4afb48e2255187096f4d223217791ef8
Author: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Date:   Mon Oct 16 15:13:25 2023 +0200

    xen-pciback: Consider INTx disabled when MSI/MSI-X is enabled
    
    [ Upstream commit 2c269f42d0f382743ab230308b836ffe5ae9b2ae ]
    
    Linux enables MSI-X before disabling INTx, but keeps MSI-X masked until
    the table is filled. Then it disables INTx just before clearing MASKALL
    bit. Currently this approach is rejected by xen-pciback.
    According to the PCIe spec, device cannot use INTx when MSI/MSI-X is
    enabled (in other words: enabling MSI/MSI-X implicitly disables INTx).
    
    Change the logic to consider INTx disabled if MSI/MSI-X is enabled. This
    applies to three places:
     - checking currently enabled interrupts type,
     - transition to MSI/MSI-X - where INTx would be implicitly disabled,
     - clearing INTx disable bit - which can be allowed even if MSI/MSI-X is
       enabled, as device should consider INTx disabled anyway in that case
    
    Fixes: 5e29500eba2a ("xen-pciback: Allow setting PCI_MSIX_FLAGS_MASKALL too")
    Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
    Acked-by: Juergen Gross <jgross@xxxxxxxx>
    Link: https://lore.kernel.org/r/20231016131348.1734721-1-marmarek@xxxxxxxxxxxxxxxxxxxxxx
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/xen/xen-pciback/conf_space.c b/drivers/xen/xen-pciback/conf_space.c
index 059de92aea7d0..d47eee6c51435 100644
--- a/drivers/xen/xen-pciback/conf_space.c
+++ b/drivers/xen/xen-pciback/conf_space.c
@@ -288,12 +288,6 @@ int xen_pcibk_get_interrupt_type(struct pci_dev *dev)
 	u16 val;
 	int ret = 0;
 
-	err = pci_read_config_word(dev, PCI_COMMAND, &val);
-	if (err)
-		return err;
-	if (!(val & PCI_COMMAND_INTX_DISABLE))
-		ret |= INTERRUPT_TYPE_INTX;
-
 	/*
 	 * Do not trust dev->msi(x)_enabled here, as enabling could be done
 	 * bypassing the pci_*msi* functions, by the qemu.
@@ -316,6 +310,19 @@ int xen_pcibk_get_interrupt_type(struct pci_dev *dev)
 		if (val & PCI_MSIX_FLAGS_ENABLE)
 			ret |= INTERRUPT_TYPE_MSIX;
 	}
+
+	/*
+	 * PCIe spec says device cannot use INTx if MSI/MSI-X is enabled,
+	 * so check for INTx only when both are disabled.
+	 */
+	if (!ret) {
+		err = pci_read_config_word(dev, PCI_COMMAND, &val);
+		if (err)
+			return err;
+		if (!(val & PCI_COMMAND_INTX_DISABLE))
+			ret |= INTERRUPT_TYPE_INTX;
+	}
+
 	return ret ?: INTERRUPT_TYPE_NONE;
 }
 
diff --git a/drivers/xen/xen-pciback/conf_space_capability.c b/drivers/xen/xen-pciback/conf_space_capability.c
index 097316a741268..1948a9700c8fa 100644
--- a/drivers/xen/xen-pciback/conf_space_capability.c
+++ b/drivers/xen/xen-pciback/conf_space_capability.c
@@ -236,10 +236,16 @@ static int msi_msix_flags_write(struct pci_dev *dev, int offset, u16 new_value,
 		return PCIBIOS_SET_FAILED;
 
 	if (new_value & field_config->enable_bit) {
-		/* don't allow enabling together with other interrupt types */
+		/*
+		 * Don't allow enabling together with other interrupt type, but do
+		 * allow enabling MSI(-X) while INTx is still active to please Linuxes
+		 * MSI(-X) startup sequence. It is safe to do, as according to PCI
+		 * spec, device with enabled MSI(-X) shouldn't use INTx.
+		 */
 		int int_type = xen_pcibk_get_interrupt_type(dev);
 
 		if (int_type == INTERRUPT_TYPE_NONE ||
+		    int_type == INTERRUPT_TYPE_INTX ||
 		    int_type == field_config->int_type)
 			goto write;
 		return PCIBIOS_SET_FAILED;
diff --git a/drivers/xen/xen-pciback/conf_space_header.c b/drivers/xen/xen-pciback/conf_space_header.c
index ac45cdc38e859..fcaa050d692d2 100644
--- a/drivers/xen/xen-pciback/conf_space_header.c
+++ b/drivers/xen/xen-pciback/conf_space_header.c
@@ -104,24 +104,9 @@ static int command_write(struct pci_dev *dev, int offset, u16 value, void *data)
 		pci_clear_mwi(dev);
 	}
 
-	if (dev_data && dev_data->allow_interrupt_control) {
-		if ((cmd->val ^ value) & PCI_COMMAND_INTX_DISABLE) {
-			if (value & PCI_COMMAND_INTX_DISABLE) {
-				pci_intx(dev, 0);
-			} else {
-				/* Do not allow enabling INTx together with MSI or MSI-X. */
-				switch (xen_pcibk_get_interrupt_type(dev)) {
-				case INTERRUPT_TYPE_NONE:
-					pci_intx(dev, 1);
-					break;
-				case INTERRUPT_TYPE_INTX:
-					break;
-				default:
-					return PCIBIOS_SET_FAILED;
-				}
-			}
-		}
-	}
+	if (dev_data && dev_data->allow_interrupt_control &&
+	    ((cmd->val ^ value) & PCI_COMMAND_INTX_DISABLE))
+		pci_intx(dev, !(value & PCI_COMMAND_INTX_DISABLE));
 
 	cmd->val = value;
 



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