linux-kernel - RE: [PATCH Part2 v6 03/49] x86/sev: Add the host SEV-SNP initialization support

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Message-ID: <SN6PR12MB2767FA7BBC983E63C2A0F0CA8E8F9@SN6PR12MB2767.namprd12.prod.outlook.com>
Date:   Tue, 19 Jul 2022 11:34:57 +0000
From:   "Kalra, Ashish" <Ashish.Kalra@....com>
To:     Borislav Petkov <bp@...en8.de>
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Subject: RE: [PATCH Part2 v6 03/49] x86/sev: Add the host SEV-SNP
 initialization support

[AMD Official Use Only - General]

Hello Boris,

>> > That section number will change over time - if you want to refer to 
>> > some section just use its title so that people can at least grep for 
>> > the relevant text.
>>
>> This will all go into sev.c, instead of the header file, as this is 
>> non-architectural and per-processor and the structure won't be exposed 
>> to the rest of the kernel. The above PPR reference and potentially in 
>> future an architectural method of reading the RMP table entries will 
>> be moved into it.

>I fail to see how this addresses my comment... All I'm saying is, the "section 2.1.4.2" number will change so don't quote it in the text but quote the section *name* instead.

Yes I agree with your comments, all I am saying is that these comments will move into sev.c instead of the header file.

>> I believe that with kexec and after issuing the shutdown command, the 
>> RMP table needs to be fully initialized, so we should be 
>> re-initializing the RMP table to zero here.

>And yet you're doing:

 >       /*
 >        * Check if SEV-SNP is already enabled, this can happen if we are coming from
 >        * kexec boot.
 >        */
 >       rdmsrl(MSR_AMD64_SYSCFG, val);
 >       if (val & MSR_AMD64_SYSCFG_SNP_EN)
 >               goto skip_enable;		<-------- skip zeroing

>So which is it?

Again what I meant is that this will be fixed to reset the RMP table for kexec boot too.

>> Yes, IOMMU is enforced for SNP to ensure that HV cannot program DMA 
>> directly into guest private memory. In case of SNP, the IOMMU makes 
>> sure that the page(s) used for DMA are HV owned.

>>Yes, now put that in the comment above the

>	fs_initcall(snp_rmptable_init);

>line.

Yes.

Thanks,
Ashish