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From: Andrew Jones <drjones@redhat.com>
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Peter Maydell <Peter.Maydell@arm.com>,
	linux-kernel@vger.kernel.org, Juan Quintela <quintela@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	qemu-devel@nongnu.org, Steven Price <steven.price@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org,
	Dave Martin <Dave.Martin@arm.com>
Subject: Re: [PATCH v2 0/2] MTE support for KVM guest
Date: Thu, 10 Sep 2020 15:39:19 +0200	[thread overview]
Message-ID: <20200910133919.rkmki6x7iscbaymh@kamzik.brq.redhat.com> (raw)
In-Reply-To: <20200910132748.GF2814@work-vm>

On Thu, Sep 10, 2020 at 02:27:48PM +0100, Dr. David Alan Gilbert wrote:
> * Andrew Jones (drjones@redhat.com) wrote:
> > On Wed, Sep 09, 2020 at 06:45:33PM -0700, Richard Henderson wrote:
> > > 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.
> > 
> > Right, as long as it's fast enough to do
> > 
> >   for_each_dirty_page(page, dirty_log)
> >     for (i = 0; i < host-page-size/16; i += 16)
> >       append_tag(LDG(page + i))
> > 
> > to get all the tags for each dirty page. I understood it would be faster
> > to use LDGM, but we'd need a new ioctl for that. So I was proposing we
> > just piggyback on a new dirty-log ioctl instead.
> 
> That feels a bad idea to me; there's a couple of different ways dirty
> page checking work; lets keep extracting the tags separate.
>

It's sounding like it was a premature optimization anyway. We don't yet
know if an ioctl for LDGM is worth it. Looping over LDG may work fine.

Thanks,
drew 


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  reply	other threads:[~2020-09-10 13:41 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-04 16:00 [PATCH v2 0/2] MTE support for KVM guest Steven Price
2020-09-04 16:00 ` [PATCH v2 1/2] arm64: kvm: Save/restore MTE registers Steven Price
2020-09-04 16:00 ` [PATCH v2 2/2] arm64: kvm: Introduce MTE VCPU feature Steven Price
2020-09-09 15:48   ` Andrew Jones
2020-09-09 15:53     ` Peter Maydell
2020-09-10  6:38       ` Andrew Jones
2020-09-10 10:01         ` Andrew Jones
2020-09-10  9:21     ` Steven Price
2020-09-10 11:49       ` Andrew Jones
2020-09-07 15:28 ` [PATCH v2 0/2] MTE support for KVM guest Dr. David Alan Gilbert
2020-09-09  9:15   ` Steven Price
2020-09-09 15:25 ` Andrew Jones
2020-09-09 16:04   ` Steven Price
2020-09-10  6:29     ` Andrew Jones
2020-09-10  9:21       ` Steven Price
2020-09-10 13:56         ` Andrew Jones
2020-09-10 14:14           ` Steven Price
2020-09-10  1:45   ` Richard Henderson
2020-09-10  5:44     ` Andrew Jones
2020-09-10 13:27       ` Dr. David Alan Gilbert
2020-09-10 13:39         ` Andrew Jones [this message]
2020-09-10  0:33 ` Richard Henderson
2020-09-10 10:24   ` Steven Price
2020-09-10 15:36     ` Richard Henderson

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