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

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Date:   Tue, 19 Jul 2022 10:38:08 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Kalra, Ashish" <Ashish.Kalra@....com>
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Subject: Re: [PATCH Part2 v6 03/49] x86/sev: Add the host SEV-SNP
 initialization support

On Tue, Jul 19, 2022 at 03:56:25AM +0000, Kalra, Ashish wrote:
> > 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.

> 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?

> 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.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette