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

Tian, Kevin
2024-04-28T06:45:21Z

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Sunday, April 28, 2024 11:20 AM
>
> 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>
> ---
> 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..57a986524502 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_dedicated_iommu;
>

what about 'no_igfx_iommu"? dedicated is implied for igfx
so a shorter name might be slightly better.

otherwise it looks good:

Reviewed-by: Kevin Tian <kevin.tian@intel.com>