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Date:   Wed, 21 Jun 2023 07:31:34 -0700
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Subject: Re: [PATCH RFC v9 07/51] x86/sev: Add the host SEV-SNP initialization
 support
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To:     Borislav Petkov <bp@alien8.de>
Cc:     Michael Roth <michael.roth@amd.com>, kvm@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        linux-crypto@vger.kernel.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
        jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com,
        ardb@kernel.org, pbonzini@redhat.com, seanjc@google.com,
        vkuznets@redhat.com, jmattson@google.com, luto@kernel.org,
        dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com,
        peterz@infradead.org, srinivas.pandruvada@linux.intel.com,
        rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com,
        vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com,
        tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com,
        dgilbert@redhat.com, jarkko@kernel.org, ashish.kalra@amd.com,
        nikunj.dadhania@amd.com, liam.merwick@oracle.com,
        zhi.a.wang@intel.com, Brijesh Singh <brijesh.singh@amd.com>
References: <20230612042559.375660-1-michael.roth@amd.com>
 <20230612042559.375660-8-michael.roth@amd.com>
 <12f95b38-427c-6810-373a-ba2062c43882@intel.com>
 <20230621091541.GEZJK/veTnfhOnX8ci@fat_crate.local>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20230621091541.GEZJK/veTnfhOnX8ci@fat_crate.local>
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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.