Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
Message-ID: <ebf3ccef-e6fe-62d5-74e8-91e30e7c2642@intel.com>
Date:   Tue, 12 Apr 2022 09:08:43 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.7.0
Content-Language: en-US
To:     David Hildenbrand <david@redhat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        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>,
        Ard Biesheuvel <ardb@kernel.org>
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>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Mike Rapoport <rppt@kernel.org>, x86@kernel.org,
        linux-mm@kvack.org, linux-coco@lists.linux.dev,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mike Rapoport <rppt@linux.ibm.com>
References: <20220405234343.74045-1-kirill.shutemov@linux.intel.com>
 <20220405234343.74045-2-kirill.shutemov@linux.intel.com>
 <93a7cfdf-02e6-6880-c563-76b01c9f41f5@intel.com>
 <ff9e0bad-be9a-97ac-ae88-d22bcfbe80d4@redhat.com>
From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCHv4 1/8] mm: Add support for unaccepted memory
In-Reply-To: <ff9e0bad-be9a-97ac-ae88-d22bcfbe80d4@redhat.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 4/12/22 01:15, David Hildenbrand wrote:
> Can we simply automate this using a kthread or smth like that, which
> just traverses the free page lists and accepts pages (similar, but
> different to free page reporting)?

That's definitely doable.

The downside is that this will force premature consumption of physical
memory resources that the guest may never use.  That's a particular
problem on TDX systems since there is no way for a VMM to reclaim guest
memory short of killing the guest.

In other words, I can see a good argument either way:
1. The kernel should accept everything to avoid the perf nastiness
2. The kernel should accept only what it needs in order to reduce memory
   use

I'm kinda partial to #1 though, if I had to pick only one.

The other option might be to tie this all to DEFERRED_STRUCT_PAGE_INIT.
 Have the rule that everything that gets a 'struct page' must be
accepted.  If you want to do delayed acceptance, you do it via
DEFERRED_STRUCT_PAGE_INIT.