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Date:   Tue, 1 Feb 2022 10:58:03 +0200
From:   Mike Rapoport <rppt@kernel.org>
To:     Michel Lespinasse <michel@lespinasse.org>
Cc:     Linux-MM <linux-mm@kvack.org>, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>, kernel-team@fb.com,
        Laurent Dufour <ldufour@linux.ibm.com>,
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        Peter Zijlstra <peterz@infradead.org>,
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        Vlastimil Babka <vbabka@suse.cz>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Matthew Wilcox <willy@infradead.org>,
        Liam Howlett <liam.howlett@oracle.com>,
        Rik van Riel <riel@surriel.com>,
        Paul McKenney <paulmck@kernel.org>,
        Song Liu <songliubraving@fb.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Minchan Kim <minchan@google.com>,
        Joel Fernandes <joelaf@google.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH v2 33/35] arm64/mm: attempt speculative mm faults first
Message-ID: <Yfj2G3oOC6cZx0IL@kernel.org>
References: <20220128131006.67712-1-michel@lespinasse.org>
 <20220128131006.67712-34-michel@lespinasse.org>
 <YfZWtsC3QIzXR0LI@kernel.org>
 <20220131080729.GA785@lespinasse.org>
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On Mon, Jan 31, 2022 at 12:07:29AM -0800, Michel Lespinasse wrote:
> On Sun, Jan 30, 2022 at 11:13:26AM +0200, Mike Rapoport wrote:
> > The speculative page fault implementation here (and for PowerPC as well)
> > looks very similar to x86. Can we factor it our rather than copy 3 (or
> > more) times?
> 
> In each arch, the speculative code was written along the lines of the
> existing non-speculative code, so that behavior would be unchanged
> when speculation succeeds.
> 
> Now each arch's existing, non-speculative code paths are quite similar,
> but they do have small differences as to how they implement various
> permission checks, protection keys and the like. The same small
> differences end up being reflected in the new speculative code paths.
> 
> I agree it would be nice if this code could be unified between archs,
> but IMO this should start with the existing non-speculative code -
> I don't think it would make sense to try unifying the new speculative
> code while trying to follow the behavior of the non-unified old
> non-speculative code paths...

Then maybe this unification can be done as the ground work for the
speculative page fault handling?

-- 
Sincerely yours,
Mike.