Re: [PATCH 1/4] iommu/amd: Check SNP support before enabling IOMMU

[Vasant Hegde]

Hi Tom,


On 1/22/2025 8:52 PM, Tom Lendacky wrote:
> On 1/21/25 19:00, Ashish Kalra wrote:
>> From: Vasant Hegde <vasant.hegde@xxxxxxx>
>>
>> iommu_snp_enable() checks for IOMMU feature support and page table
>> compatibility. Ideally this check should be done before enabling
>> IOMMUs. Currently its done after enabling IOMMUs. Also its causes
> 
> Why should it be done before enabling the IOMMUs? In other words, at
> some more detail here.

Sure. Basically IOMMU enable stage checks for SNP support. I will update it.

> 
>> issue if kvm_amd is builtin.
>>
>> Hence move SNP enable check before enabling IOMMUs.
>>
>> Fixes: 04d65a9dbb33 ("iommu/amd: Don't rely on external callers to enable IOMMU SNP support")
>> Cc: Ashish Kalra <ashish.kalra@xxxxxxx>
>> Signed-off-by: Vasant Hegde <vasant.hegde@xxxxxxx>
> 
> Ashish, as the submitter, this requires your Signed-off-by:.
> 
>> ---
>>  drivers/iommu/amd/init.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
>> index c5cd92edada0..419a0bc8eeea 100644
>> --- a/drivers/iommu/amd/init.c
>> +++ b/drivers/iommu/amd/init.c
>> @@ -3256,13 +3256,14 @@ static int __init state_next(void)
>>  		}
>>  		break;
>>  	case IOMMU_ACPI_FINISHED:
>> +		/* SNP enable has to be called after early_amd_iommu_init() */
> 
> This comment doesn't really explain anything, so I think it should
> either be improved or just remove it.

Sure. I will remove it.

-Vasant