PCI/MSI: Handle the NOMASK flag correctly for all PCI/MSI backends

The conversion of the XEN specific global variable pci_msi_ignore_mask to a
MSI domain flag, missed the facts that:

    1) Legacy architectures do not provide a interrupt domain
    2) Parent MSI domains do not necessarily have a domain info attached
   
Both cases result in an unconditional NULL pointer dereference. This was
unfortunatly missed in review and testing revealed it late.

Cure this by using the existing pci_msi_domain_supports() helper, which
handles all possible cases correctly.

Fixes: c3164d2 ("PCI/MSI: Convert pci_msi_ignore_mask to per MSI domain flag")
Reported-by: Daniel Gomez <da.gomez@kernel.org>
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Borislav Petkov <bp@alien8.de>
Tested-by: Daniel Gomez <da.gomez@kernel.org>
Link: https://lore.kernel.org/all/87iknwyp2o.ffs@tglx
Closes: https://lore.kernel.org/all/qn7fzggcj6qe6r6gdbwcz23pzdz2jx64aldccmsuheabhmjgrt@tawf5nfwuvw7

Author: KAGA-KOKO

drivers/pci/msi/msi.c

@@ -285,8 +285,6 @@ static void pci_msi_set_enable(struct pci_dev *dev, int enable)
 static int msi_setup_msi_desc(struct pci_dev *dev, int nvec,
 			      struct irq_affinity_desc *masks)
 {
-	const struct irq_domain *d = dev_get_msi_domain(&dev->dev);
-	const struct msi_domain_info *info = d->host_data;
 	struct msi_desc desc;
 	u16 control;
 
@@ -297,7 +295,7 @@ static int msi_setup_msi_desc(struct pci_dev *dev, int nvec,
 	/* Lies, damned lies, and MSIs */
 	if (dev->dev_flags & PCI_DEV_FLAGS_HAS_MSI_MASKING)
 		control |= PCI_MSI_FLAGS_MASKBIT;
-	if (info->flags & MSI_FLAG_NO_MASK)
+	if (pci_msi_domain_supports(dev, MSI_FLAG_NO_MASK, DENY_LEGACY))
 		control &= ~PCI_MSI_FLAGS_MASKBIT;
 
 	desc.nvec_used			= nvec;
@@ -604,20 +602,18 @@ static void __iomem *msix_map_region(struct pci_dev *dev,
  */
 void msix_prepare_msi_desc(struct pci_dev *dev, struct msi_desc *desc)
 {
-	const struct irq_domain *d = dev_get_msi_domain(&dev->dev);
-	const struct msi_domain_info *info = d->host_data;
-
 	desc->nvec_used				= 1;
 	desc->pci.msi_attrib.is_msix		= 1;
 	desc->pci.msi_attrib.is_64		= 1;
 	desc->pci.msi_attrib.default_irq	= dev->irq;
 	desc->pci.mask_base			= dev->msix_base;
-	desc->pci.msi_attrib.can_mask		= !(info->flags & MSI_FLAG_NO_MASK) &&
-						  !desc->pci.msi_attrib.is_virtual;
 
-	if (desc->pci.msi_attrib.can_mask) {
+
+	if (!pci_msi_domain_supports(dev, MSI_FLAG_NO_MASK, DENY_LEGACY) &&
+	    !desc->pci.msi_attrib.is_virtual) {
 		void __iomem *addr = pci_msix_desc_addr(desc);
 
+		desc->pci.msi_attrib.can_mask = 1;
 		desc->pci.msix_ctrl = readl(addr + PCI_MSIX_ENTRY_VECTOR_CTRL);
 	}
 }
@@ -715,8 +711,6 @@ static int msix_setup_interrupts(struct pci_dev *dev, struct msix_entry *entries
 static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
 				int nvec, struct irq_affinity *affd)
 {
-	const struct irq_domain *d = dev_get_msi_domain(&dev->dev);
-	const struct msi_domain_info *info = d->host_data;
 	int ret, tsize;
 	u16 control;
 
@@ -747,7 +741,7 @@ static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
 	/* Disable INTX */
 	pci_intx_for_msi(dev, 0);
 
-	if (!(info->flags & MSI_FLAG_NO_MASK)) {
+	if (!pci_msi_domain_supports(dev, MSI_FLAG_NO_MASK, DENY_LEGACY)) {
 		/*
 		 * Ensure that all table entries are masked to prevent
 		 * stale entries from firing in a crash kernel.