[PATCH 1/1] iommu/vt-d: Decouple igfx_off from graphic identity mapping

Lu Baolu
2024-05-03T13:37:37Z

A kernel command called igfx_off was introduced in commit <ba39592764ed>
("Intel IOMMU: Intel IOMMU driver"). This command allows the user to
disable the IOMMU dedicated to SOC-integrated graphic devices.

Commit <9452618e7462> ("iommu/intel: disable DMAR for g4x integrated gfx")
used this mechanism to disable the graphic-dedicated IOMMU for some
problematic devices. Later, more problematic graphic devices were added
to the list by commit <1f76249cc3beb> ("iommu/vt-d: Declare Broadwell igfx
dmar support snafu").

On the other hand, commit <19943b0e30b05> ("intel-iommu: Unify hardware
and software passthrough support") uses the identity domain for graphic
devices if CONFIG_DMAR_BROKEN_GFX_WA is selected.

+ if (iommu_pass_through)
+ iommu_identity_mapping = 1;
+#ifdef CONFIG_DMAR_BROKEN_GFX_WA
+ else
+ iommu_identity_mapping = 2;
+#endif
...

static int iommu_should_identity_map(struct pci_dev *pdev, int startup)
{
+ if (iommu_identity_mapping == 2)
+ return IS_GFX_DEVICE(pdev);
...

In the following driver evolution, CONFIG_DMAR_BROKEN_GFX_WA and
quirk_iommu_igfx() are mixed together, causing confusion in the driver's
device_def_domain_type callback. On one hand, dmar_map_gfx is used to turn
off the graphic-dedicated IOMMU as a workaround for some buggy hardware;
on the other hand, for those graphic devices, IDENTITY mapping is required
for the IOMMU core.

Commit <4b8d18c0c986> "iommu/vt-d: Remove INTEL_IOMMU_BROKEN_GFX_WA" has
removed the CONFIG_DMAR_BROKEN_GFX_WA option, so the IDENTITY_DOMAIN
requirement for graphic devices is no longer needed. Therefore, this
requirement can be removed from device_def_domain_type() and igfx_off can
be made independent.

Fixes: 4b8d18c0c986 ("iommu/vt-d: Remove INTEL_IOMMU_BROKEN_GFX_WA")
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240428032020.214616-1-baolu.lu@linux.intel.com
---
drivers/iommu/intel/iommu.c | 19 ++++++-------------
1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index fbbf8fda22f3..2e9811bf2a4e 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -217,12 +217,11 @@ int intel_iommu_sm = IS_ENABLED(CONFIG_INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON);
int intel_iommu_enabled = 0;
EXPORT_SYMBOL_GPL(intel_iommu_enabled);

-static int dmar_map_gfx = 1;
static int intel_iommu_superpage = 1;
static int iommu_identity_mapping;
static int iommu_skip_te_disable;
+static int disable_igfx_iommu;

-#define IDENTMAP_GFX 2
#define IDENTMAP_AZALIA 4

const struct iommu_ops intel_iommu_ops;
@@ -261,7 +260,7 @@ static int __init intel_iommu_setup(char *str)
no_platform_optin = 1;
pr_info("IOMMU disabled\n");
} else if (!strncmp(str, "igfx_off", 8)) {
- dmar_map_gfx = 0;
+ disable_igfx_iommu = 1;
pr_info("Disable GFX device mapping\n");
} else if (!strncmp(str, "forcedac", 8)) {
pr_warn("intel_iommu=forcedac deprecated; use iommu.forcedac instead\n");
@@ -2196,9 +2195,6 @@ static int device_def_domain_type(struct device *dev)

if ((iommu_identity_mapping & IDENTMAP_AZALIA) && IS_AZALIA(pdev))
return IOMMU_DOMAIN_IDENTITY;
-
- if ((iommu_identity_mapping & IDENTMAP_GFX) && IS_GFX_DEVICE(pdev))
- return IOMMU_DOMAIN_IDENTITY;
}

return 0;
@@ -2499,9 +2495,6 @@ static int __init init_dmars(void)
iommu_set_root_entry(iommu);
}

- if (!dmar_map_gfx)
- iommu_identity_mapping |= IDENTMAP_GFX;
-
check_tylersburg_isoch();

ret = si_domain_init(hw_pass_through);
@@ -2592,7 +2585,7 @@ static void __init init_no_remapping_devices(void)
/* This IOMMU has *only* gfx devices. Either bypass it or
set the gfx_mapped flag, as appropriate */
drhd->gfx_dedicated = 1;
- if (!dmar_map_gfx)
+ if (disable_igfx_iommu)
drhd->ignored = 1;
}
}
@@ -4621,7 +4614,7 @@ static void quirk_iommu_igfx(struct pci_dev *dev)
return;

pci_info(dev, "Disabling IOMMU for graphics on this chipset\n");
- dmar_map_gfx = 0;
+ disable_igfx_iommu = 1;
}

/* G4x/GM45 integrated gfx dmar support is totally busted. */
@@ -4702,8 +4695,8 @@ static void quirk_calpella_no_shadow_gtt(struct pci_dev *dev)

if (!(ggc & GGC_MEMORY_VT_ENABLED)) {
pci_info(dev, "BIOS has allocated no shadow GTT; disabling IOMMU for graphics\n");
- dmar_map_gfx = 0;
- } else if (dmar_map_gfx) {
+ disable_igfx_iommu = 1;
+ } else if (!disable_igfx_iommu) {
/* we have to ensure the gfx device is idle before we flush */
pci_info(dev, "Disabling batched IOTLB flush on Ironlake\n");
iommu_set_dma_strict();
--
2.34.1