linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Decouple igfx

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Message-ID: <850146ff-ce6f-44b3-9326-d44d29550b34@linux.intel.com>
Date: Sun, 28 Apr 2024 20:12:56 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>, "Wang, Zhenyu Z" <zhenyu.z.wang@...el.com>
Cc: baolu.lu@...ux.intel.com, "iommu@...ts.linux.dev"
 <iommu@...ts.linux.dev>,
 "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] iommu/vt-d: Decouple igfx_off from graphic identity
 mapping

On 2024/4/28 14:45, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@...ux.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@...ux.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.

I like disable_igfx_iommu more. :-)

Best regards,
baolu