linux-kernel - Re: [PATCH RFC v9 07/51] x86/sev: Add the host SEV-SNP initialization support

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Date:   Wed, 21 Jun 2023 07:31:34 -0700
From:   Dave Hansen <dave.hansen@...el.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,
        dgilbert@...hat.com, jarkko@...nel.org, ashish.kalra@....com,
        nikunj.dadhania@....com, liam.merwick@...cle.com,
        zhi.a.wang@...el.com, Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH RFC v9 07/51] x86/sev: Add the host SEV-SNP initialization
 support

On 6/21/23 02:15, Borislav Petkov wrote:
> On Mon, Jun 12, 2023 at 08:34:02AM -0700, Dave Hansen wrote:
>> On 6/11/23 21:25, Michael Roth wrote:
>>> +	/*
>>> +	 * Calculate the amount the memory that must be reserved by the BIOS to
>>> +	 * address the whole RAM, including the bookkeeping area. The RMP itself
>>> +	 * must also be covered.
>>> +	 */
>>> +	max_rmp_pfn = max_pfn;
>>> +	if (PHYS_PFN(rmp_end) > max_pfn)
>>> +		max_rmp_pfn = PHYS_PFN(rmp_end);
>> Could you say a little here about how this deals with memory hotplug?
> Does SNP hw even support memory hotplug?
> 
> I think in order to support that, you'd need some special dance because
> of the RMP table etc...

Yep, there's the hardware side and then there are fun nuggets like using
mem= and then doing a software-only hot-add later after boot.

Also, if the hardware doesn't support any kind of hotplug, it would be
great to point to the place in the spec where it says that.