linux-kernel - Re: [PATCH v4 0/8] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag

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Date:   Wed, 27 Jan 2021 17:16:06 +0000
From:   Will Deacon <will@...nel.org>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Jan Kara <jack@...e.cz>, Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        kernel-team@...roid.com
Subject: Re: [PATCH v4 0/8] Create 'old' ptes for faultaround mappings on
 arm64 with hardware access flag

On Tue, Jan 26, 2021 at 03:28:22PM -0800, Hugh Dickins wrote:
> On Tue, 26 Jan 2021, Will Deacon wrote:
> > On Wed, Jan 20, 2021 at 05:36:04PM +0000, Will Deacon wrote:
> > > Hi all,
> > > 
> > > This is version four of the patches I previously posted here:
> > > 
> > >   v1: https://lore.kernel.org/r/20201209163950.8494-1-will@kernel.org
> > >   v2: https://lore.kernel.org/r/20210108171517.5290-1-will@kernel.org
> > >   v3: https://lore.kernel.org/r/20210114175934.13070-1-will@kernel.org
> > > 
> > > The patches allow architectures to opt-in at runtime for faultaround
> > > mappings to be created as 'old' instead of 'young'. Although there have
> > > been previous attempts at this, they failed either because the decision
> > > was deferred to userspace [1] or because it was done unconditionally and
> > > shown to regress benchmarks for particular architectures [2].
> > > 
> > > The big change since v3 is that the immutable fields of 'struct vm_fault'
> > > now live in a 'const' anonymous struct. Although Clang will silently
> > > accept modifications to these fields [3], GCC emits an error. The
> > > resulting diffstat is _considerably_ more manageable with this approach.
> > 
> > The only changes I have pending against this series are cosmetic (commit
> > logs). Can I go ahead and queue this in the arm64 tree so that it can sit
> > in linux-next for a bit? (positive or negative feedback appreciated!).
> 
> That would be fine by me: I ran v3 on rc3, then the nicer smaller v4
> on rc4, and saw no problems when running either of them (x86_64 only).

Thanks, Hugh. I'll stick these into -next later today and we'll see how we
get on.

Will