Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <X/d2DyLfXZmBIreY@redhat.com> <CAHk-=wjs9v-hp_7HV_TrTmisu7pNX=MwZ62ZV82i0evLhPwS1Q@mail.gmail.com>
 <X/eLwQPd5bi620Vt@redhat.com> <CAHk-=whjS3pUZRJLR_HdgB0_1Sd4gWXUbLLyShKxOg0ySCdnUA@mail.gmail.com>
 <CAHk-=wgRZ5o5pUqKC6cwTLU=V-G+rF5DTexGh1kCMGrgXDufew@mail.gmail.com>
 <X/edsWgguQDgsOtx@redhat.com> <CAHk-=whTCBa6Frpbveuy7Hnz17P+g03yQvynkApFbBjV5rVrsA@mail.gmail.com>
 <20210108124815.GA4512@willie-the-truck> <X/iEyk0ijxhSvs9T@redhat.com>
 <CAHk-=wizOEqJTomh=K5CR300mtTCwWdj+QYYCXKHaiU-R0YE9Q@mail.gmail.com> <X/icBLF59bREm97b@redhat.com>
In-Reply-To: <X/icBLF59bREm97b@redhat.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 8 Jan 2021 11:25:21 -0800
Message-ID: <CAHk-=wjf-GwbXgDm8RDkW1ctajzDst4dp2LOZSd3+m7Ojo5vDA@mail.gmail.com>
Subject: Re: [PATCH 2/2] mm: soft_dirty: userfaultfd: introduce wrprotect_tlb_flush_pending
To:     Andrea Arcangeli <aarcange@redhat.com>
Cc:     Will Deacon <will@kernel.org>, Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Yu Zhao <yuzhao@google.com>, Andy Lutomirski <luto@kernel.org>,
        Peter Xu <peterx@redhat.com>,
        Pavel Emelyanov <xemul@openvz.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Minchan Kim <minchan@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Leon Romanovsky <leonro@nvidia.com>,
        Jason Gunthorpe <jgg@ziepe.ca>, Jan Kara <jack@suse.cz>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Jan 8, 2021 at 9:53 AM Andrea Arcangeli <aarcange@redhat.com> wrote:
>
> Do you intend to eventually fix the zygote vmsplice case or not?
> Because in current upstream it's not fixed currently using the
> enterprise default config.

Is this the hugepage case? Neither of your patches actually touched
that, so I've forgotten the details.

> Irrelevant special case as in: long term GUP pin on the memory?

Irrelevant special case in that

 (a) an extra COW shouldn't be a correctness issue unless somebody
does something horribly wrong (and obviously the code that hasn't
taken the mmap_lock for writing are then examples of that)

and

 (b) it's not a performance issue either unless you can find a real
load that does it.

Hmm?

               Linus