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

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Message-ID: <5df43bd9-e154-4227-9202-bd72b794fdfb@amd.com>
Date: Wed, 22 Jan 2025 22:37:25 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Tom Lendacky <thomas.lendacky@....com>,
 Ashish Kalra <Ashish.Kalra@....com>, seanjc@...gle.com, pbonzini@...hat.com,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 john.allen@....com, herbert@...dor.apana.org.au, davem@...emloft.net,
 joro@...tes.org, suravee.suthikulpanit@....com, will@...nel.org,
 robin.murphy@....com
Cc: michael.roth@....com, dionnaglaze@...gle.com, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
 linux-coco@...ts.linux.dev, iommu@...ts.linux.dev
Subject: Re: [PATCH 1/4] iommu/amd: Check SNP support before enabling IOMMU

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@....com>
>>
>> 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@....com>
>> Signed-off-by: Vasant Hegde <vasant.hegde@....com>
> 
> 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