linux-kernel - Re: [RFC PATCH v2 1/2] mm/userfaultfd: fix memory corruption due to writeprotect

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Date:   Tue, 5 Jan 2021 20:06:22 +0000
From:   Nadav Amit <namit@...are.com>
To:     Andrea Arcangeli <aarcange@...hat.com>
CC:     Peter Xu <peterx@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-mm <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>, Yu Zhao <yuzhao@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Pavel Emelyanov <xemul@...nvz.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Minchan Kim <minchan@...nel.org>,
        Will Deacon <will@...nel.org>, Mel Gorman <mgorman@...e.de>
Subject: Re: [RFC PATCH v2 1/2] mm/userfaultfd: fix memory corruption due to
 writeprotect

> On Jan 5, 2021, at 11:45 AM, Andrea Arcangeli <aarcange@...hat.com> wrote:
> 
> On Tue, Jan 05, 2021 at 07:05:22PM +0000, Nadav Amit wrote:
>>> On Jan 5, 2021, at 10:45 AM, Andrea Arcangeli <aarcange@...hat.com> wrote:
>>> I just don't like to slow down a feature required in the future for
>>> implementing postcopy live snapshotting or other snapshots to userland
>>> processes (for the non-KVM case, also unprivileged by default if using
>>> bounce buffers to feed the syscalls) that can be used by open source
>>> hypervisors to beat proprietary hypervisors like vmware.
>> 
>> Ouch, that’s uncalled for. I am sure that you understand that I have no
>> hidden agenda and we all have the same goal.
> 
> Ehm I never said you had an hidden agenda, so I'm not exactly why
> you're accusing me of something I never said.
> 
> I merely pointed out one relevant justification for increasing kernel
> complexity here by not slowing down clear_refs longstanding O(N)
> clear_refs/softdirty feature and the recent uffd-wp O(1) feature, is
> to be more competitive with proprietary software solutions, since
> at least for uffd-wp, postcopy live snapshotting that the #1 use
> case.
> 
> I never questioned your contribution or your preference, to be even
> more explicit, it never crossed my mind that you have an hidden
> agenda.
> 
> However since everyone already acked your patches and I'm not ok with
> your patches because they will give a hit to KVM postcopy live
> snapshotting and other container clear_refs users, I have to justify
> why I NAK your patches and remaining competitive with proprietary
> hypervisors is one of them, so I don't see what is wrong to state a
> tangible end goal here.

I fully understand your objection to my patches and it is a valid
objection, which I will address.

I just thought that there might be some insinuation, as you mentioned VMware
by name. My response was half-jokingly and should have had a smiley to
prevent you from wasting your time on the explanation.