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Subject: Re: [PATCH v2 0/2] MTE support for KVM guest
To:     Andrew Jones <drjones@redhat.com>,
        Steven Price <steven.price@arm.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
        "Dr. David Alan Gilbert" <dgilbert@redhat.com>,
        Peter Maydell <Peter.Maydell@arm.com>, qemu-devel@nongnu.org,
        Dave Martin <Dave.Martin@arm.com>,
        Juan Quintela <quintela@redhat.com>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org
References: <20200904160018.29481-1-steven.price@arm.com>
 <20200909152540.ylnrljd6aelxoxrf@kamzik.brq.redhat.com>
From:   Richard Henderson <richard.henderson@linaro.org>
Message-ID: <5cb1d7ed-54a5-4337-6c3d-2e3e7df89f17@linaro.org>
Date:   Wed, 9 Sep 2020 18:45:33 -0700
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On 9/9/20 8:25 AM, Andrew Jones wrote:
>>  * Provide a KVM-specific method to extract the tags from guest memory.
>>    This might also have benefits in terms of providing an easy way to
>>    read bulk tag data from guest memory (since the LDGM instruction
>>    isn't available at EL0).
> 
> Maybe we need a new version of KVM_GET_DIRTY_LOG that also provides
> the tags for all addresses of each dirty page.

KVM_GET_DIRTY_LOG just provides one bit per dirty page, no?  Then VMM copies
the data out from its local address to guest memory.

There'd be no difference with or without tags, afaik.  It's just about how VMM
copies the data, with or without tags.

>>  * Provide support for user space setting the TCMA0 or TCMA1 bits in
>>    TCR_EL1. These would allow the VMM to generate pointers which are not
>>    tag checked.
> 
> So this is necessary to allow the VMM to keep tag checking enabled for
> itself, plus map guest memory as PROT_MTE, and write to that memory when
> needed? 

I don't see a requirement for the VMM to set TCMA0.


r~