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Subject: Re: [RFC PATCH v8 5/5] KVM: arm64: ioctl to fetch/store tags in a
 guest
To:     Peter Maydell <peter.maydell@linaro.org>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        kvmarm <kvmarm@lists.cs.columbia.edu>,
        arm-mail-list <linux-arm-kernel@lists.infradead.org>,
        lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dave Martin <Dave.Martin@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        QEMU Developers <qemu-devel@nongnu.org>,
        Juan Quintela <quintela@redhat.com>,
        "Dr. David Alan Gilbert" <dgilbert@redhat.com>,
        Richard Henderson <richard.henderson@linaro.org>,
        Haibo Xu <Haibo.Xu@arm.com>, Andrew Jones <drjones@redhat.com>
References: <20210205135803.48321-1-steven.price@arm.com>
 <20210205135803.48321-6-steven.price@arm.com>
 <CAFEAcA99kV_d6ev9wC4ySiyoD7Cp=HCD0v2bBhGSOU-KrzkqaQ@mail.gmail.com>
From:   Steven Price <steven.price@arm.com>
Message-ID: <1e09d70a-1443-c7bd-2d16-f50bc3993a83@arm.com>
Date:   Wed, 10 Feb 2021 16:03:34 +0000
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On 08/02/2021 17:31, Peter Maydell wrote:
> On Fri, 5 Feb 2021 at 13:58, Steven Price <steven.price@arm.com> wrote:
>>
>> The VMM may not wish to have it's own mapping of guest memory mapped
>> with PROT_MTE because this causes problems if the VMM has tag checking
>> enabled (the guest controls the tags in physical RAM and it's unlikely
>> the tags are correct for the VMM).
>>
>> Instead add a new ioctl which allows the VMM to easily read/write the
>> tags from guest memory, allowing the VMM's mapping to be non-PROT_MTE
>> while the VMM can still read/write the tags for the purpose of
>> migration.
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>>   arch/arm64/include/uapi/asm/kvm.h | 13 +++++++
>>   arch/arm64/kvm/arm.c              | 57 +++++++++++++++++++++++++++++++
>>   include/uapi/linux/kvm.h          |  1 +
>>   3 files changed, 71 insertions(+)
> 
> Missing the update to the docs in Documentation/virtual/kvm/api.txt :-)

Good point - although I was secretly hoping to get some feedback on the 
concepts before writing the documentation! But I guess the documentation 
will help with the review. I'll include some in the next posting.

Thanks,

Steve