linux-kernel - Re: [RFC][PATCH v2 14/21] kvm: register in mm

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Message-ID: <f23265d4-528e-3bd4-011f-4d7b8f3281db@redhat.com>
Date:   Mon, 4 Feb 2019 11:46:54 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Xu <peterx@...hat.com>, Fengguang Wu <fengguang.wu@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Nikita Leshenko <nikita.leshchenko@...cle.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        kvm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Fan Du <fan.du@...el.com>, Yao Yuan <yuan.yao@...el.com>,
        Peng Dong <dongx.peng@...el.com>,
        Huang Ying <ying.huang@...el.com>,
        Liu Jingqi <jingqi.liu@...el.com>,
        Dong Eddie <eddie.dong@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Zhang Yi <yi.z.zhang@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [RFC][PATCH v2 14/21] kvm: register in mm_struct

On 02/02/19 07:57, Peter Xu wrote:
> 
> I'm thinking whether it's legal for multiple VMs to run on a single mm
> address space.  I don't see a limitation so far but it's very possible
> I am just missing something there (if there is, IMHO they might be
> something nice to put into the commit message?).  Thanks,

Yes, it certainly is legal, and even useful in fact.

For example there are people running WebAssembly in a KVM sandbox.  In
that case you can have multiple KVM instances in a single process.

It seems to me that there is already a perfect way to link an mm to its
users, which is the MMU notifier.  Why do you need a separate
proc_ept_idle_operations?  You could change ept_idle_read into an MMU
notifier callback, and have core mm/ core combine the output of
mm_idle_read and all the MMU notifiers?  Basically, ept_idle_ctrl
becomes an argument to the new MMU notifier callback, or something like
that.

Paolo