iommu: Update "iommu.strict" documentation

Consolidating the flush queue logic also meant that the "iommu.strict"
option started taking effect on x86 as well. Make sure we document that.

Fixes: a250c23f15c2 ("iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/2c8c06e1b449d6b060c5bf9ad3b403cd142f405d.1623682646.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbd..20a32de 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1987,7 +1987,7 @@
                          forcing Dual Address Cycle for PCI cards supporting
                          greater than 32-bit addressing.
 
-       iommu.strict=   [ARM64] Configure TLB invalidation behaviour
+       iommu.strict=   [ARM64, X86] Configure TLB invalidation behaviour
                        Format: { "0" | "1" }
                        0 - Lazy mode.
                          Request that DMA unmap operations use deferred
@@ -1998,6 +1998,10 @@
                        1 - Strict mode (default).
                          DMA unmap operations invalidate IOMMU hardware TLBs
                          synchronously.
+                       Note: on x86, the default behaviour depends on the
+                       equivalent driver-specific parameters, but a strict
+                       mode explicitly specified by either method takes
+                       precedence.
 
        iommu.passthrough=
                        [ARM64, X86] Configure DMA to bypass the IOMMU by default.