Message-ID: <9fce601e-b557-4454-8698-6c63303999a1@linux.intel.com>
Date: Fri, 18 Apr 2025 11:07:16 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Mingcong Bai <jeffbai@...c.io>
Cc: intel-gfx@...ts.freedesktop.org, kexybiscuit@...c.io,
 Wenhao Sun <weiguangtwk@...look.com>, David Woodhouse <dwmw2@...radead.org>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH RESEND] iommu: intel: apply quirk_iommu_igfx for
 8086:0044 (QM57/QS57)

On 1/20/25 17:35, Mingcong Bai wrote:
> (I'm not very confident about the approach of this patch but I failed to
> find a better way to address the issue I have on hand, so please consider
> this patch as an RFC...)
> 
> On the Lenovo ThinkPad X201, when Intel VT-d is enabled in the BIOS, the
> kernel boots with errors related to DMAR, the graphical interface appeared
> quite choppy, and the system resets erratically within a minute after it
> booted:
> 
> DMAR: DRHD: handling fault status reg 3
> DMAR: [DMA Write NO_PASID] Request device [00:02.0] fault addr 0xb97ff000
> [fault reason 0x05] PTE Write access is not set
> 
> Upon comparing boot logs with VT-d on/off, I found that the Intel Calpella
> quirk (`quirk_calpella_no_shadow_gtt()') correctly applied the igfx IOMMU
> disable/quirk correctly:
> 
> pci 0000:00:00.0: DMAR: BIOS has allocated no shadow GTT; disabling IOMMU
> for graphics
> 
> Whereas with VT-d on, it went into the "else" branch, which then
> triggered the DMAR handling fault above:
> 
> ... 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();
> }
> 
> Now, this is not exactly scientific, but moving 0x0044 to quirk_iommu_igfx
> seems to have fixed the aforementioned issue. Running a few `git blame'
> runs on the function, I have found that the quirk was originally
> introduced as a fix specific to ThinkPad X201:
> 
> commit 9eecabcb9a92 ("intel-iommu: Abort IOMMU setup for igfx if BIOS gave
> no shadow GTT space")
> 
> Which was later revised twice to the "else" branch we saw above:
> 
> - 2011: commit 6fbcfb3e467a ("intel-iommu: Workaround IOTLB hang on
>    Ironlake GPU")
> - 2024: commit ba00196ca41c ("iommu/vt-d: Decouple igfx_off from graphic
>    identity mapping")
> 
> I'm uncertain whether further testings on this particular laptops were
> done in 2011 and (honestly I'm not sure) 2024, but I would be happy to do
> some distro-specific testing if that's what would be required to verify
> this patch.
> 
> P.S., I also see IDs 0x0040, 0x0062, and 0x006a listed under the same
> `quirk_calpella_no_shadow_gtt()' quirk, but I'm not sure how similar these
> chipsets are (if they share the same issue with VT-d or even, indeed, if
> this issue is specific to a bug in the Lenovo BIOS). With regards to
> 0x0062, it seems to be a Centrino wireless card, but not a chipset?
> 
> I have also listed a couple (distro and kernel) bug reports below as
> references (some of them are from 7-8 years ago!), as they seem to be
> similar issue found on different Westmere/Ironlake, Haswell, and Broadwell
> hardware setups.
> 
> Link:https://bugzilla.kernel.org/show_bug.cgi?id=197029
> Link:https://groups.google.com/g/qubes-users/c/4NP4goUds2c?pli=1
> Link:https://bugs.archlinux.org/task/65362
> Link:https://bbs.archlinux.org/viewtopic.php?id=230323
> Reported-by: Wenhao Sun<weiguangtwk@...look.com>
> Signed-off-by: Mingcong Bai<jeffbai@...c.io>
> ---
>   drivers/iommu/intel/iommu.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)

Queued for v6.15-rc. Thank you!

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