[PATCH] iommu/amd: Add amd_iommu=force_enable option

From: Joerg Roedel
Date: Thu Jun 03 2021 - 09:02:08 EST


From: Joerg Roedel <jroedel@xxxxxxx>

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@xxxxxxx>
Acked-by: Alex Deucher <alexander.deucher@xxxxxxx>
---
Documentation/admin-guide/kernel-parameters.txt | 3 +++
drivers/iommu/amd/init.c | 9 ++++++++-
2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbdedc46..f6bf4e87df80 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -301,6 +301,9 @@
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 d006724f4dc2..23614337abef 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -153,7 +153,8 @@ int amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_VAPIC;
static int amd_iommu_xt_mode = IRQ_REMAP_XAPIC_MODE;

static bool amd_iommu_detected;
-static bool __initdata amd_iommu_disabled;
+static bool amd_iommu_disabled __initdata;
+static bool amd_iommu_force_enable __initdata;
static int amd_iommu_target_ivhd_type;

u16 amd_iommu_last_bdf; /* largest PCI device id we have
@@ -2834,6 +2835,9 @@ 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;
@@ -2845,6 +2849,7 @@ static bool detect_ivrs(void)
}
}

+out:
/* Make sure ACS will be enabled during PCI probe */
pci_request_acs();

@@ -3100,6 +3105,8 @@ 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