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

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Date:   Mon, 1 Jun 2020 22:10:09 +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

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:

diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index 5b81fd16f5fa..b07458cc1b0b 100644
--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -1875,6 +1875,8 @@ static int __init amd_iommu_init_pci(void)
                 ret = iommu_init_pci(iommu);
                 if (ret)
                         break;
+               iommu_flush_all_caches(iommu);
+               init_iommu_perf_ctr(iommu);
         }

         /*
--
2.17.1

Thanks,
Suravee