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

Nadav Amit
2021-01-05T20:07:32Z

> On Jan 5, 2021, at 11:45 AM, Andrea Arcangeli <aarcange@redhat.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@redhat.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.