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

[Hugh Dickins <hughd@google.com>]

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).

Hugh