[PATCH 4.19 078/196] PCI: hv: Return zero, not garbage, when reading PCI_INTERRUPT_PIN

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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Wei Liu <wei.liu@xxxxxxxxxx>

commit fea93a3e5d5e6a09eb153866d2ce60ea3287a70d upstream.

The intent of the code snippet is to always return 0 for both
PCI_INTERRUPT_LINE and PCI_INTERRUPT_PIN.

The check misses PCI_INTERRUPT_PIN. This patch fixes that.

This is discovered by this call in VFIO:

    pci_read_config_byte(vdev->pdev, PCI_INTERRUPT_PIN, &pin);

The old code does not set *val to 0 because it misses the check for
PCI_INTERRUPT_PIN. Garbage is returned in that case.

Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Link: https://lore.kernel.org/linux-pci/20240701202606.129606-1-wei.liu@xxxxxxxxxx
Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@xxxxxxxxxx>
Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/pci/controller/pci-hyperv.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -650,8 +650,8 @@ static void _hv_pcifront_read_config(str
 		   PCI_CAPABILITY_LIST) {
 		/* ROM BARs are unimplemented */
 		*val = 0;
-	} else if (where >= PCI_INTERRUPT_LINE && where + size <=
-		   PCI_INTERRUPT_PIN) {
+	} else if ((where >= PCI_INTERRUPT_LINE && where + size <= PCI_INTERRUPT_PIN) ||
+		   (where >= PCI_INTERRUPT_PIN && where + size <= PCI_MIN_GNT)) {
 		/*
 		 * Interrupt Line and Interrupt PIN are hard-wired to zero
 		 * because this front-end only supports message-signaled






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