AMD IOMMU: add parameter to disable device isolation

Impact: add a new AMD IOMMU kernel command line parameter
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

Documentation/kernel-parameters.txt

@@ -295,6 +295,8 @@ and is between 256 and 4096 characters. It is defined in the file
 			isolate - enable device isolation (each device, as far
 			          as possible, will get its own protection
 			          domain)
+			share - put every device behind one IOMMU into the
+				same protection domain
 			fullflush - enable flushing of IO/TLB entries when
 				    they are unmapped. Otherwise they are
 				    flushed before they will be reused, which

arch/x86/kernel/amd_iommu_init.c

@@ -1213,6 +1213,8 @@ static int __init parse_amd_iommu_options(char *str)
 	for (; *str; ++str) {
 		if (strncmp(str, "isolate", 7) == 0)
 			amd_iommu_isolate = 1;
+		if (strncmp(str, "share", 5) == 0)
+			amd_iommu_isolate = 0;
 		if (strncmp(str, "fullflush", 11) == 0)
 			amd_iommu_unmap_flush = true;
 	}