linux-kernel - Re: [PATCHv6 11/30] x86/tdx: Handle in-kernel MMIO

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Message-ID: <87o824241q.ffs@tglx>
Date:   Thu, 17 Mar 2022 12:48:17 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Hansen <dave.hansen@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        mingo@...hat.com, bp@...en8.de, luto@...nel.org,
        peterz@...radead.org
Cc:     sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        thomas.lendacky@....com, brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv6 11/30] x86/tdx: Handle in-kernel MMIO

On Wed, Mar 16 2022 at 14:53, Dave Hansen wrote:
> On 3/15/22 19:08, Kirill A. Shutemov wrote:
>> In other words, even if all of the work was done to paravirtualize all
>> x86 MMIO users and virtio, this approach would still be needed. There
>> is essentially no way to get rid of this code.
> ...
>> == Patching TDX drivers ==
> ...> This approach will be adopted in the future, removing the bulk of
>> MMIO #VEs. The #VE-based MMIO will remain serving non-virtio use cases.
>
> I still don't like this very much, but I can't argue with my own logic. :)
>
> BTW, TDX folks...  I expect you to, today, start coming up with a
> comprehensive list of the MMIO-induced #VE's and the reasoning why they
> should or should not be paravirtualized.  You're going to get grumpy
> maintainers if this is done haphazardly as one-offs when users hit
> performance issues.

Grumpy maintainers? That's a meme. I've never seen that happen. :)