linux-kernel - Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization support

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Message-ID: <f6e36ffd-86e4-49cf-40d7-a289b444fe3e@amd.com>
Date:   Wed, 8 Nov 2023 13:53:10 -0600
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Michael Roth <michael.roth@....com>, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
        dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
        peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
        rientjes@...gle.com, dovmurik@...ux.ibm.com, tobin@....com,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        jarkko@...nel.org, nikunj.dadhania@....com, pankaj.gupta@....com,
        liam.merwick@...cle.com, zhi.a.wang@...el.com,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization
 support

On 11/8/2023 12:14 AM, Borislav Petkov wrote:
> On Tue, Nov 07, 2023 at 04:33:41PM -0600, Kalra, Ashish wrote:
>> We will still need some method to tell the IOMMU driver if SNP
>> support/feature is disabled by this function, for example, when CPU family
>> and model is not supported by SNP and we jump to no_snp label.
> 
> See below.
> 
>> The reliable way for this to work is to ensure snp_rmptable_init() is called
>> before IOMMU initialization and then IOMMU initialization depends on SNP
>> feature flag setup by snp_rmptable_init() to enable SNP support on IOMMU or
>> not.
> 
> Yes, this whole SNP initialization needs to be reworked and split this
> way:
> 
> - early detection work which needs to be done once goes to
>    bsp_init_amd(): that's basically your early_detect_mem_encrypt() stuff
>    which needs to happen exactly only once and early.
> 
> - Any work like:
> 
> 	 c->x86_phys_bits -= (cpuid_ebx(0x8000001f) >> 6) & 0x3f;
> 
>    and the like which needs to happen on each AP, gets put in a function
>    which gets called by init_amd().
> 
> By the time IOMMU gets to init, you already know whether it should
> enable SNP and check X86_FEATURE_SEV_SNP.
> 
> Finally, you call __snp_rmptable_init() which does the *per-CPU* init
> work which is still pending. >
> Ok?	

Yes, will need to rework the SNP initialization stuff, the important 
point is that we want to do snp_rmptable_init() stuff before IOMMU 
initialization as for things like RMP table not correctly setup, etc., 
we don't want IOMMU initialization to enable SNP on the IOMMUs.

Thanks,
Ashish