iommu/amd: Fix a stale comment about which legacy mode is user visible

[ Upstream commit 4bf53c2 ]

Update a stale comment about which of the legacy modes is visible to the
user, i.e. can be forced via amd_iommu_intr=legacy.

Fixes: b74aa02 ("iommu/amd: Fix legacy interrupt remapping for x2APIC-enabled system")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Wei Wang <wei.w.wang@hotmail.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: sean-jc

drivers/iommu/amd/amd_iommu_types.h

@@ -906,12 +906,13 @@ static inline int get_hpet_devid(int id)
 }
 
 enum amd_iommu_intr_mode_type {
-	AMD_IOMMU_GUEST_IR_LEGACY,
-
-	/* This mode is not visible to users. It is used when
-	 * we cannot fully enable vAPIC and fallback to only support
-	 * legacy interrupt remapping via 128-bit IRTE.
+	/*
+	 * The legacy format mode is not visible to users to prevent the user
+	 * from crashing x2APIC systems, which for all intents and purposes
+	 * require 128-bit IRTEs.   The legacy format will be forced as needed
+	 * when hardware doesn't support 128-bit IRTEs.
 	 */
+	AMD_IOMMU_GUEST_IR_LEGACY,
 	AMD_IOMMU_GUEST_IR_LEGACY_GA,
 	AMD_IOMMU_GUEST_IR_VAPIC,
 };