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

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Message-ID: <alpine.LNX.2.20.13.2006152346320.21123@monopod.intra.ispras.ru>
Date:   Mon, 15 Jun 2020 23:48:52 +0300 (MSK)
From:   Alexander Monakov <amonakov@...ras.ru>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>
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 Mon, 1 Jun 2020, Suravee Suthikulpanit 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

> 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
>