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SubjectRe: [PATCH] iommu/amd: Fix event counter availability check
Hi,

Adding Shuah Khan to Cc: I've noticed you've seen this issue on Ryzen 2400GE;
can you have a look at the patch? Would be nice to know if it fixes the
problem for you too.

Thanks.
Alexander

On Fri, 29 May 2020, Alexander Monakov wrote:

> The driver performs an extra check if the IOMMU's capabilities advertise
> presence of performance counters: it verifies that counters are writable
> by writing a hard-coded value to a counter and testing that reading that
> counter gives back the same value.
>
> Unfortunately it does so quite early, even before pci_enable_device is
> called for the IOMMU, i.e. when accessing its MMIO space is not
> guaranteed to work. On Ryzen 4500U CPU, this actually breaks the test:
> the driver assumes the counters are not writable, and disables the
> functionality.
>
> 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.
>
> Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> Cc: iommu@lists.linux-foundation.org
> ---
>
> PS. I'm seeing another hiccup with IOMMU probing on my system:
> pci 0000:00:00.2: can't derive routing for PCI INT A
> pci 0000:00:00.2: PCI INT A: not connected
>
> Hopefully I can figure it out, but I'd appreciate hints.
>
> drivers/iommu/amd_iommu_init.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
> index 5b81fd16f5fa..1b7ec6b6a282 100644
> --- a/drivers/iommu/amd_iommu_init.c
> +++ b/drivers/iommu/amd_iommu_init.c
> @@ -1788,8 +1788,6 @@ static int __init iommu_init_pci(struct amd_iommu *iommu)
> if (iommu->cap & (1UL << IOMMU_CAP_NPCACHE))
> amd_iommu_np_cache = true;
>
> - init_iommu_perf_ctr(iommu);
> -
> if (is_rd890_iommu(iommu->dev)) {
> int i, j;
>
> @@ -1891,8 +1889,10 @@ static int __init amd_iommu_init_pci(void)
>
> init_device_table_dma();
>
> - for_each_iommu(iommu)
> + for_each_iommu(iommu) {
> iommu_flush_all_caches(iommu);
> + init_iommu_perf_ctr(iommu);
> + }
>
> if (!ret)
> print_iommu_info();
>
> base-commit: 75caf310d16cc5e2f851c048cd597f5437013368
>

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