linux-kernel - Re: [PATCH] iommu/amd: Fix event counter availability check

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Date:   Tue, 16 Jun 2020 16:35:48 +0700
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     Alexander Monakov <amonakov@...ras.ru>
Cc:     linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org
Subject: Re: [PATCH] iommu/amd: Fix event counter availability check



On 6/16/20 3:48 AM, Alexander Monakov wrote:
>> Alexander
>>
>> On 6/1/20 4:01 PM, Alexander Monakov wrote:
>>> On Mon, 1 Jun 2020, Suravee Suthikulpanit wrote:
>>>
>>>>> Moving init_iommu_perf_ctr just after iommu_flush_all_caches resolves
>>>>> the issue. This is the earliest point in amd_iommu_init_pci where the
>>>>> call succeeds on my laptop.
>>>> According to your description, it should just need to be anywhere after
>>>> the
>>>> pci_enable_device() is called for the IOMMU device, isn't it? So, on your
>>>> system, what if we just move the init_iommu_perf_ctr() here:
>>> No, this doesn't work, as I already said in the paragraph you are responding
>>> to. See my last sentence in the quoted part.
>>>
>>> So the implication is init_device_table_dma together with subsequent cache
>>> flush is also setting up something that is necessary for counters to be
>>> writable.
>>>
>>> Alexander
>>>
>> Instead of blindly moving the code around to a spot that would just work,
>> I am trying to understand what might be required here. In this case,
>> the init_device_table_dma()should not be needed. I suspect it's the IOMMU
>> invalidate all command that's also needed here.
>>
>> I'm also checking with the HW and BIOS team. Meanwhile, could you please give
>> the following change a try:
> Hello. Can you give any update please?
> 
> Alexander
> 

Sorry for late reply. I have a reproducer and working with the HW team to understand the issue.
I should be able to provide update with solution by the end of this week.

Suravee