linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Fix kdump kernels boot failure with scalable mode

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Message-ID: <ed90e585-d5e8-15b6-6285-67ecc53f05ca@linux.intel.com>
Date:   Fri, 12 Aug 2022 11:43:50 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jerry Snitselaar <jsnitsel@...hat.com>
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux.dev,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>, Wen Jin <wen.jin@...el.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Fix kdump kernels boot failure with
 scalable mode

Hi Jerry,

On 2022/8/9 00:21, Jerry Snitselaar wrote:
> On Mon, Aug 08, 2022 at 11:46:12AM +0800, Lu Baolu wrote:
>> The translation table copying code for kdump kernels is currently based
>> on the extended root/context entry formats of ECS mode defined in older
>> VT-d v2.5, and doesn't handle the scalable mode formats. This causes
>> the kexec capture kernel boot failure with DMAR faults if the IOMMU was
>> enabled in scalable mode by the previous kernel.
>>
>> The ECS mode has already been deprecated by the VT-d spec since v3.0 and
>> Intel IOMMU driver doesn't support this mode as there's no real hardware
>> implementation. Hence this converts ECS checking in copying table code
>> into scalable mode.
>>
>> The existing copying code consumes a bit in the context entry as a mark
>> of copied entry. This marker needs to work for the old format as well as
>> for extended context entries. It's hard to find such a bit for both
>> legacy and scalable mode context entries. This replaces it with a per-
>> IOMMU bitmap.
>>
>> Fixes: 7373a8cc38197 ("iommu/vt-d: Setup context and enable RID2PASID support")
>> Cc:stable@...r.kernel.org
>> Reported-by: Jerry Snitselaar<jsnitsel@...hat.com>
>> Tested-by: Wen Jin<wen.jin@...el.com>
>> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
>> ---
> I did a quick test last night, and it was able to harvest the vmcore,
> and boot back up. Before you mentioned part of the issue being that it
> couldn't get to the PGTT field in the pasid table entry. Was that not
> the case, 

It is the case from IOMMU hardware point of view.

> or is it looking at the old kernel pasid dir entries and
> table entries through the pasid dir pointer in the copied context
> entry?

Yes. It reuses the pasid table in old kernel and replaces it until the
new device driver takes over and starts the first DMA operation.

Best regards,
baolu