linux-kernel - Re: [PATCH v3 7/7] iommu/amd: Do not support IOMMUv2 APIs when SNP is enabled

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Date:   Wed, 29 Jun 2022 18:54:34 +0700
From:   "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        robin.murphy@....com, ashish.kalra@....com, vasant.hegde@....com,
        thomas.lendacky@....com
Subject: Re: [PATCH v3 7/7] iommu/amd: Do not support IOMMUv2 APIs when SNP is
 enabled



On 6/23/2022 3:23 PM, Joerg Roedel wrote:
> On Wed, Jun 22, 2022 at 12:11:31PM -0500, Suravee Suthikulpanit wrote:
>>   bool amd_iommu_v2_supported(void)
>>   {
>> -	return amd_iommu_v2_present;
>> +	/*
>> +	 * Since DTE[Mode]=0 is prohibited on SNP-enabled system
>> +	 * (i.e. EFR[SNPSup]=1), IOMMUv2 page table cannot be used without
>> +	 * setting up IOMMUv1 page table.
>> +	 */
>> +	return amd_iommu_v2_present && !amd_iommu_snp_en;
> 
> IOMMU_v2 APIs could actually be supported with GIOV and IOMMUv2
> page-tables in-use, no?
> 
We can support IOMMUv2 iff the v1 table is also setup (i.e. DTE[Mode] != 0).
Currently w/ IOMMU_v2 APIs, the IOMMU sets the mode to zero. Therefore, we
cannot support this use case.

Best Regards,
Suravee