Re: [PATCH v2 4/4] iommu/amd: Enable Host SNP support after enabling IOMMU SNP support

[Vasant Hegde <vasant.hegde@amd.com>]

Hi ,

On 1/31/2025 7:18 AM, Sean Christopherson wrote:
> On Fri, Jan 31, 2025, Ashish Kalra wrote:
>> From: Sean Christopherson <seanjc@google.com>
>>
>> This patch fixes the current SNP host enabling code and effectively SNP
>   ^^^^^^^^^^
>> ---
>>  drivers/iommu/amd/init.c | 18 ++++++++++++++----
>>  1 file changed, 14 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
>> index c5cd92edada0..ee887aa4442f 100644
>> --- a/drivers/iommu/amd/init.c
>> +++ b/drivers/iommu/amd/init.c
>> @@ -3194,7 +3194,7 @@ static bool __init detect_ivrs(void)
>>  	return true;
>>  }
>>  
>> -static void iommu_snp_enable(void)
>> +static __init void iommu_snp_enable(void)
> 
> If you're feeling nitpicky, adding "__init" could be done in a separate patch.
> 
>>  {
>>  #ifdef CONFIG_KVM_AMD_SEV
>>  	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
>> @@ -3219,6 +3219,11 @@ static void iommu_snp_enable(void)
>>  		goto disable_snp;
>>  	}
>>  
>> +	if (snp_rmptable_init()) {
>> +		pr_warn("SNP: RMP initialization failed, SNP cannot be supported.\n");
>> +		goto disable_snp;
>> +	}
>> +
>>  	pr_info("IOMMU SNP support enabled.\n");
>>  	return;
>>  
>> @@ -3426,18 +3431,23 @@ void __init amd_iommu_detect(void)
>>  	int ret;
>>  
>>  	if (no_iommu || (iommu_detected && !gart_iommu_aperture))
>> -		return;
>> +		goto disable_snp;
>>  
>>  	if (!amd_iommu_sme_check())
>> -		return;
>> +		goto disable_snp;
>>  
>>  	ret = iommu_go_to_state(IOMMU_IVRS_DETECTED);
>>  	if (ret)
>> -		return;
>> +		goto disable_snp;
> 
> This handles initial failure, but it won't handle the case where amd_iommu_prepare()
> fails, as the iommu_go_to_state() call from amd_iommu_enable() will get
> short-circuited.  I don't see any pleasant options.  Maybe this?
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index c5cd92edada0..436e47f13f8f 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3318,6 +3318,8 @@ static int __init iommu_go_to_state(enum iommu_init_state state)
>                 ret = state_next();
>         }
>  
> +       if (ret && !amd_iommu_snp_en && cc_platform_has(CC_ATTR_HOST_SEV_SNP))

I think we should clear when `amd_iommu_snp_en` is true. May be below check is
enough?

	if (ret && amd_iommu_snp_en)


-Vasant