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Date:   Mon, 7 Dec 2020 10:06:22 +0700
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     Jerry Snitselaar <jsnitsel@...hat.com>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: Re: [PATCH] iommu/amd: Increase interrupt remapping table limit to
 512 entries

Jerry,

On 12/2/20 6:53 AM, Jerry Snitselaar wrote:
> 
> Suravee Suthikulpanit @ 2020-10-14 19:50 MST:
> 
>> 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 {
> 
> With this change should DTE_IRQ_TABLE_LEN be changed to 9? IIUC the spec
> correctly leaving it at 8 is saying the table is 256 entries long.

You are correct. Sorry I missed this part. I'll send the fix-up patch ASAP.

Thank you,
Suravee

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