linux-kernel - Re: [RFC] KVM: mm: fd-based approach for supporting KVM guest private memory

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Message-Id: <73319f3c-6f5e-4f39-a678-7be5fddd55f2@www.fastmail.com>
Date:   Fri, 27 Aug 2021 11:24:13 -0700
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "David Hildenbrand" <david@...hat.com>,
        "Sean Christopherson" <seanjc@...gle.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>
Cc:     "Vitaly Kuznetsov" <vkuznets@...hat.com>,
        "Wanpeng Li" <wanpengli@...cent.com>,
        "Jim Mattson" <jmattson@...gle.com>,
        "Joerg Roedel" <joro@...tes.org>, "kvm list" <kvm@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "Borislav Petkov" <bp@...en8.de>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Joerg Roedel" <jroedel@...e.de>,
        "Andi Kleen" <ak@...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 (Intel)" <peterz@...radead.org>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Varad Gautam" <varad.gautam@...e.com>,
        "Dario Faggioli" <dfaggioli@...e.com>,
        "the arch/x86 maintainers" <x86@...nel.org>, linux-mm@...ck.org,
        linux-coco@...ts.linux.dev,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        "Sathyanarayanan Kuppuswamy" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Dave Hansen" <dave.hansen@...el.com>,
        "Yu Zhang" <yu.c.zhang@...ux.intel.com>
Subject: Re: [RFC] KVM: mm: fd-based approach for supporting KVM guest private memory



On Thu, Aug 26, 2021, at 2:26 PM, David Hildenbrand wrote:
> On 26.08.21 19:05, Andy Lutomirski wrote:

> > Oof.  That's quite a requirement.  What's the point of the VMA once all
> > this is done?
> 
> You can keep using things like mbind(), madvise(), ... and the GUP code 
> with a special flag might mostly just do what you want. You won't have 
> to reinvent too many wheels on the page fault logic side at least.
> 

You can keep calling the functions.  The implementations working is a different story: you can't just unmap (pte_numa-style or otherwise) a private guest page to quiesce it, move it with memcpy(), and then fault it back in.

In any event, adding fd-based NUMA APIs would be quite nice.  Look at the numactl command.