[PATCH] iommu/vt-d: Fix kernel panic caused by 416fa531c816: Preset Access/Dirty bits for IOVA over FL

["Joerg M. Sigle" <joerg.sigle@jsigle.com>]

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From: Joerg M. Sigle <joerg.sigle@jsigle.com>

Patch 416fa531c816 commit 416fa531c8160151090206a51b829b9218b804d9 caused
an immediate kernel panic on boot at RIP: 0010:__domain_mapping+0xa7/0x3a0
with longterm kernel 5.10.37 configured w/ CONFIG_INTEL_IOMMU_DEFAULT_ON=y
due to removal of a check. Putting the check back in place fixes this.
The kernel panic was observed on various Intel Core i7 i5 i3 CPUs from
Sandy Bridge, Haswell, Broadwell and Kaby Lake generations (at least).
It may NOT be reproducible on some older CPU generations.
Suppressing the panic with boot parameter intel_iommu=off is diagnostic.
See: https://bugzilla.kernel.org/show_bug.cgi?id=213077
https://bugzilla.kernel.org/show_bug.cgi?id=213087
https://bugzilla.kernel.org/show_bug.cgi?id=213095

Signed-off-by: Joerg M. Sigle <joerg.sigle@jsigle.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>

---

Dear colleagues,

Please find the suggested patch in the attachment, now reformatted to include the affected C function.
It fixes a problem in LT kernel 5.10.37; I'm asking for inclusion into LT kernel 5.10.38.

I'm submitting this now, after receiving Lu Baolu's positive response attached below.
Baolu, I hope that the line "Acked-by: Lu Baolu ..." is ok given your comment.

I hope I'm providing this in a useful way, following
https://www.kernel.org/doc/html/v4.17/process/submitting-patches.html

I'm still unsure whether this line should be added above:
Cc: stable@vger.kernel.org
Please add this if needed, also considering Baolu's comment re. upstream/backported.

Thanks and kind regards to all! Joerg


Am 17.05.2021 um 04:51 schrieb Lu Baolu:
> Hi Joerg,
> 
> On 5/16/21 7:57 AM, Joerg M. Sigle wrote:
>> Dear colleagues at Intel
>>
>> could you please check the enclosed bug report
>> and confirm whether the suggested patch is valid.
>>
>> Thank you very much & kind regards - Joerg
>>
>>
>> -------- Weitergeleitete Nachricht --------
>> From: bugzilla-daemon@bugzilla.kernel.org
>> To: joerg.sigle@jsigle.com
>> Subject: [Bug 213077] Kernel 5.10.37 immediately panics at boot w/ Intel Core i7-4910MQ Haswell or Core i3-5010U Broadwell w/ custom .config CONFIG_INTEL_IOMMU_DEFAULT_ON=y, same config worked with 5.10.36, due to commit 416fa531c816 =
>> a8ce9ebbecdfda3322bbcece6b3b25888217f8e3
>> Date: Sat, 15 May 2021 23:47:39 +0000
>> X-Envelope-To: joerg.sigle@jsigle.com
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=213077
>>
>> --- Comment #7 from Joerg M. Sigle (joerg.sigle@jsigle.com) ---
>> This patch:
>>
>> 416fa531c816 iommu/vt-d: Preset Access/Dirty bits for IOVA over FL
>> commit 416fa531c8160151090206a51b829b9218b804d9
>> Upstream commit a8ce9ebbecdfda3322bbcece6b3b25888217f8e3
>>
>> https://github.com/arter97/x86-kernel/commit/416fa531c8160151090206a51b829b9218b804d9
>>
>> while doing other things, changed the conditional:
>>
>> if (!sg) { ...
>>          sg_res = nr_pages;
>>          pteval = ((phys_addr_t)phys_pfn << VTD_PAGE_SHIFT) | attr;
>> }
>>
>> to an unconditional:
>>
>> pteval = ((phys_addr_t)phys_pfn << VTD_PAGE_SHIFT) | attr;
>>
>> Reinserting the check for !sg fixed the immediate panic on boot for me.
>> Reverting the remainder of the same patch had not helped before.
>>
>> Here's a possible patch for 5.10.37:
>>
>> -------------------------------------------------------------------------
>> --- a/drivers/iommu/intel/iommu.c       2021-05-14 09:50:46.000000000 +0200
>> +++ b/drivers/iommu/intel/iommu.c       2021-05-16 01:02:17.816810690 +0200
>> @@ -2373,7 +2373,10 @@
>>                  }
>>          }
>>
>> -       pteval = ((phys_addr_t)phys_pfn << VTD_PAGE_SHIFT) | attr;
>> +        if (!sg) {
>> +                sg_res = nr_pages;
>> +                pteval = ((phys_addr_t)phys_pfn << VTD_PAGE_SHIFT) | attr;
>> +       }
>>
>>          while (nr_pages > 0) {
>>                  uint64_t tmp;
>> -------------------------------------------------------------------------
>>
>> Could you please check this patch submission and pass it to upstream?
> 
> 
> Above fix looks good to me.
> 
> This issue is caused by the back-ported patch for stable v5.10.37.
> There's no need for upstream.
> 
> Best regards,
> baolu
> 
>>
>> I have, however, NOT tried to understand what the code really does.
>> So please ask the suppliers of patch 416fa531c816 whether their
>> removal of the condition was intentional or a mere lapsus. Thanks!
>>
>> Thanks and kind regards, Joerg
>>
> 

-- 
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Dr. med. Jörg M. Sigle                             +41 76 276 86 94
http://www.ql-recorder.com                         +41 32 510 23 46
http://www.jsigle.com                           +49 176 96 43 54 13

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--- a/drivers/iommu/intel/iommu.c	2021-05-14 09:50:46.000000000 +0200
+++ b/drivers/iommu/intel/iommu.c	2021-05-16 01:02:17.816810690 +0200
@@ -2373,7 +2373,10 @@ static int __domain_mapping(struct dmar_
 		}
 	}
 
-	pteval = ((phys_addr_t)phys_pfn << VTD_PAGE_SHIFT) | attr;
+	if (!sg) {
+                sg_res = nr_pages;
+                pteval = ((phys_addr_t)phys_pfn << VTD_PAGE_SHIFT) | attr;
+	}
 
 	while (nr_pages > 0) {
 		uint64_t tmp;