linux-kernel - Re: [PATCH v5 0/2] MTE support for KVM guest

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Message-ID: <6b9072fb-1232-e9fb-0b97-e69709980f99@linaro.org>
Date:   Wed, 9 Dec 2020 14:13:05 -0600
From:   Richard Henderson <richard.henderson@...aro.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Marc Zyngier <maz@...nel.org>, Steven Price <steven.price@....com>,
        Peter Maydell <peter.maydell@...aro.org>,
        Haibo Xu <haibo.xu@...aro.org>,
        lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Juan Quintela <quintela@...hat.com>,
        QEMU Developers <qemu-devel@...gnu.org>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
        Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH v5 0/2] MTE support for KVM guest

On 12/9/20 12:39 PM, Catalin Marinas wrote:
>> I would have thought that the best way is to use TCO, so that we don't have to
>> have dual mappings (and however many MB of extra page tables that might imply).
> 
> The problem appears when the VMM wants to use MTE itself (e.g. linked
> against an MTE-aware glibc), toggling TCO is no longer generic enough,
> especially when it comes to device emulation.

But we do know exactly when we're manipulating guest memory -- we have special
routines for that.  So the special routines gain a toggle of TCO around the
exact guest memory manipulation, not a blanket disable of MTE across large
swaths of QEMU.


r~