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Date:   Tue, 10 Aug 2021 10:36:21 -0700
From:   Dave Hansen <>
To:     "Kirill A. Shutemov" <>
Cc:     "Kirill A. Shutemov" <>,
        Borislav Petkov <>,
        Andy Lutomirski <>,
        Sean Christopherson <>,
        Andrew Morton <>,
        Joerg Roedel <>,
        Andi Kleen <>,
        Kuppuswamy Sathyanarayanan 
        David Rientjes <>,
        Vlastimil Babka <>,
        Tom Lendacky <>,
        Thomas Gleixner <>,
        Peter Zijlstra <>,
        Paolo Bonzini <>,
        Ingo Molnar <>,
        Varad Gautam <>,
        Dario Faggioli <>,,,,
Subject: Re: [PATCH 0/5] x86: Impplement support for unaccepted memory

On 8/10/21 10:31 AM, Kirill A. Shutemov wrote:
> On Tue, Aug 10, 2021 at 08:51:01AM -0700, Dave Hansen wrote:
>> Let's say we have a 128GB VM.  How much does faster does this approach
>> reach userspace than if all memory was accepted up front?  How much
>> memory _could_ have been accepted at the point userspace starts running?
> Acceptance code is not optimized yet: we accept memory in 4k chunk which
> is very slow because hypercall overhead dominates the picture.
> As of now, kernel boot time of 1 VCPU and 64TiB VM with upfront memory
> accept is >20 times slower than with this lazy memory accept approach.

That's a pretty big deal.

> 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?

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