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

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Message-ID: <20210810175144.uqlddcicyrweqb4j@black.fi.intel.com>
Date:   Tue, 10 Aug 2021 20:51:44 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Varad Gautam <varad.gautam@...e.com>,
        Dario Faggioli <dfaggioli@...e.com>, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] x86: Impplement support for unaccepted memory

On Tue, Aug 10, 2021 at 10:36:21AM -0700, Dave Hansen wrote:
> > The difference is going to be substantially lower once we get it optimized
> > properly.
> 
> What does this mean?  Is this future work in the kernel or somewhere in
> the TDX hardware/firmware which will speed things up?

Kernel has to be changed to accept memory in 2M and 1G chunks where
possible. The interface exists and described in spec, but not yet used in
guest kernel.

It would cut hypercall overhead dramatically. It makes upfront memory
accept more bearable and lowers latency of lazy memory accept. So I expect
the gap being not 20x, but like 3-5x (which is still huge).

-- 
 Kirill A. Shutemov