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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Dave Hansen <dave.hansen@intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        mingo@redhat.com, bp@alien8.de, luto@kernel.org,
        peterz@infradead.org
Cc:     sathyanarayanan.kuppuswamy@linux.intel.com, aarcange@redhat.com,
        ak@linux.intel.com, dan.j.williams@intel.com, david@redhat.com,
        hpa@zytor.com, jgross@suse.com, jmattson@google.com,
        joro@8bytes.org, jpoimboe@redhat.com, knsathya@kernel.org,
        pbonzini@redhat.com, sdeep@vmware.com, seanjc@google.com,
        tony.luck@intel.com, vkuznets@redhat.com, wanpengli@tencent.com,
        thomas.lendacky@amd.com, brijesh.singh@amd.com, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCHv6 11/30] x86/tdx: Handle in-kernel MMIO
In-Reply-To: <b1c1c4f1-8e5d-3c5a-8433-e101bbf79600@intel.com>
References: <20220316020856.24435-1-kirill.shutemov@linux.intel.com>
 <20220316020856.24435-12-kirill.shutemov@linux.intel.com>
 <b1c1c4f1-8e5d-3c5a-8433-e101bbf79600@intel.com>
Date:   Thu, 17 Mar 2022 12:48:17 +0100
Message-ID: <87o824241q.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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. :)