linux-kernel - [PATCH] iommu/amd: Add amd_iommu=force

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Date:   Thu, 22 Apr 2021 15:07:01 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     iommu@...ts.linux-foundation.org
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        alexander.deucher@....com, d1nuc0m@...tonmail.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <jroedel@...e.de>
Subject: [PATCH] iommu/amd: Add amd_iommu=force_enable option

From: Joerg Roedel <jroedel@...e.de>

Add this option to enable the IOMMU on platforms like AMD Stoney,
where the kernel usually disables it because it may cause problems in
some scenarios.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 Documentation/admin-guide/kernel-parameters.txt | 3 +++
 drivers/iommu/amd/init.c                        | 7 +++++++
 2 files changed, 10 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 04545725f187..c9573f726707 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -303,6 +303,9 @@
 					  allowed anymore to lift isolation
 					  requirements as needed. This option
 					  does not override iommu=pt
+			force_enable - Force enable the IOMMU on platforms known
+				       to be buggy with IOMMU enabled. Use this
+				       option with care.
 
 	amd_iommu_dump=	[HW,X86-64]
 			Enable AMD IOMMU driver option to dump the ACPI table
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 321f5906e6ed..3e2295d3b3e2 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -155,6 +155,7 @@ static int amd_iommu_xt_mode = IRQ_REMAP_XAPIC_MODE;
 
 static bool amd_iommu_detected;
 static bool __initdata amd_iommu_disabled;
+static bool __initdata amd_iommu_force_enable;
 static int amd_iommu_target_ivhd_type;
 
 u16 amd_iommu_last_bdf;			/* largest PCI device id we have
@@ -2882,6 +2883,9 @@ static bool detect_ivrs(void)
 
 	acpi_put_table(ivrs_base);
 
+	if (amd_iommu_force_enable)
+		goto out;
+
 	/* Don't use IOMMU if there is Stoney Ridge graphics */
 	for (i = 0; i < 32; i++) {
 		u32 pci_id;
@@ -2893,6 +2897,7 @@ static bool detect_ivrs(void)
 		}
 	}
 
+out:
 	/* Make sure ACS will be enabled during PCI probe */
 	pci_request_acs();
 
@@ -3148,6 +3153,8 @@ static int __init parse_amd_iommu_options(char *str)
 	for (; *str; ++str) {
 		if (strncmp(str, "fullflush", 9) == 0)
 			amd_iommu_unmap_flush = true;
+		if (strncmp(str, "force_enable", 12) == 0)
+			amd_iommu_force_enable = true;
 		if (strncmp(str, "off", 3) == 0)
 			amd_iommu_disabled = true;
 		if (strncmp(str, "force_isolation", 15) == 0)
-- 
2.31.1