Re: [PATCH 0/5] x86: Impplement support for unaccepted memory

From: Dave Hansen <dave.hansen@intel.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
	Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
	Sean Christopherson <seanjc@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Joerg Roedel <jroedel@suse.de>
Cc: Andi Kleen <ak@linux.intel.com>,
	Kuppuswamy Sathyanarayanan
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ingo Molnar <mingo@redhat.com>,
	Varad Gautam <varad.gautam@suse.com>,
	Dario Faggioli <dfaggioli@suse.com>,
	x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev,
	linux-kernel@vger.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH 0/5] x86: Impplement support for unaccepted memory
Date: Tue, 10 Aug 2021 07:08:58 -0700	[thread overview]
Message-ID: <4b80289a-07a4-bf92-9946-b0a8afb27326@intel.com> (raw)
In-Reply-To: <20210810062626.1012-1-kirill.shutemov@linux.intel.com>

On 8/9/21 11:26 PM, Kirill A. Shutemov wrote:
> UEFI Specification version 2.9 introduces concept of memory acceptance:
> Some Virtual Machine platforms, such as Intel TDX or AMD SEV-SNP,
> requiring memory to be accepted before it can be used by the guest.
> Accepting happens via a protocol specific for the Virtrual Machine
> platform.
> 
> Accepting memory is costly and it makes VMM allocate memory for the
> accepted guest physical address range. We don't want to accept all memory
> upfront.

This could use a bit more explanation.  Any VM is likely to *eventually*
touch all its memory, so it's not like a VMM has a long-term advantage
by delaying this.

So, it must have to do with resource use at boot.  Is this to help boot
times?

I had expected this series, but I also expected it to be connected to
CONFIG_DEFERRED_STRUCT_PAGE_INIT somehow.  Could you explain a bit how
this problem is different and demands a totally orthogonal solution?

For instance, what prevents us from declaring: "Memory is accepted at
the time that its 'struct page' is initialized" ?  Then, we use all the
infrastructure we already have for DEFERRED_STRUCT_PAGE_INIT.

This series isn't too onerous, but I do want to make sure that we're not
reinventing the wheel.