linux-kernel - Re: [PATCH] iommu/amd: Increase interrupt remapping table limit to 512 entries

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Date:   Mon, 26 Oct 2020 09:14:21 +0700
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Cc:     joro@...tes.org
Subject: Re: [PATCH] iommu/amd: Increase interrupt remapping table limit to
 512 entries

Hi Joerg,

Do you have any concerns regarding this patch?

Thanks,
Suravee

On 10/15/20 9:50 AM, Suravee Suthikulpanit wrote:
> Certain device drivers allocate IO queues on a per-cpu basis.
> On AMD EPYC platform, which can support up-to 256 cpu threads,
> this can exceed the current MAX_IRQ_PER_TABLE limit of 256,
> and result in the error message:
> 
>      AMD-Vi: Failed to allocate IRTE
> 
> This has been observed with certain NVME devices.
> 
> AMD IOMMU hardware can actually support upto 512 interrupt
> remapping table entries. Therefore, update the driver to
> match the hardware limit.
> 
> Please note that this also increases the size of interrupt remapping
> table to 8KB per device when using the 128-bit IRTE format.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>   drivers/iommu/amd/amd_iommu_types.h | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
> index 30a5d412255a..427484c45589 100644
> --- a/drivers/iommu/amd/amd_iommu_types.h
> +++ b/drivers/iommu/amd/amd_iommu_types.h
> @@ -406,7 +406,11 @@ extern bool amd_iommu_np_cache;
>   /* Only true if all IOMMUs support device IOTLBs */
>   extern bool amd_iommu_iotlb_sup;
>   
> -#define MAX_IRQS_PER_TABLE	256
> +/*
> + * AMD IOMMU hardware only support 512 IRTEs despite
> + * the architectural limitation of 2048 entries.
> + */
> +#define MAX_IRQS_PER_TABLE	512
>   #define IRQ_TABLE_ALIGNMENT	128
>   
>   struct irq_remap_table {
>