x86: Ignore iommu=off for AMD cpus

The kdump config scripts add the iommu=off kernel parameter which is
problematic on AMD hardware. Just ignore it.

Add an iommu=forceoff option in case anybody really wants to disable iommu
on AMD.

Orabug: 34779071

Signed-off-by: Dave Kleikamp <[email protected]>
Reviewed-by: Darren Kenny <[email protected]>

Author: kleikamp

arch/x86/kernel/pci-dma.c

@@ -120,7 +120,13 @@ static __init int iommu_setup(char *p)
 		return -EINVAL;
 
 	while (*p) {
-		if (!strncmp(p, "off", 3))
+		if (!strncmp(p, "off", 3)) {
+			if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
+				pr_warn("iommu=off ignored on AMD. Use iommu=forceoff if you really mean it\n");
+			else
+				no_iommu = 1;
+		}
+		if (!strncmp(p, "forceoff", 8))
 			no_iommu = 1;
 		/* gart_parse_options has more force support */
 		if (!strncmp(p, "force", 5))