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Date:   Sat, 29 Aug 2020 08:02:30 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        linux-mm <linux-mm@kvack.org>,
        Linux API <linux-api@vger.kernel.org>,
        Oleksandr Natalenko <oleksandr@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Tim Murray <timmurray@google.com>,
        Sandeep Patil <sspatil@google.com>,
        Sonny Rao <sonnyrao@google.com>,
        Brian Geffon <bgeffon@google.com>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shakeel Butt <shakeelb@google.com>,
        John Dias <joaodias@google.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Jann Horn <jannh@google.com>,
        alexander.h.duyck@linux.intel.com,
        SeongJae Park <sj38.park@gmail.com>,
        David Rientjes <rientjes@google.com>,
        Arjun Roy <arjunroy@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Christian Brauner <christian@brauner.io>,
        Daniel Colascione <dancol@google.com>,
        Jens Axboe <axboe@kernel.dk>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        SeongJae Park <sjpark@amazon.de>,
        linux-man <linux-man@vger.kernel.org>
Subject: Re: [PATCH v8 3/4] mm/madvise: introduce process_madvise() syscall:
 an external memory hinting API
Message-ID: <20200829070230.GA1099@infradead.org>
References: <20200622192900.22757-1-minchan@kernel.org>
 <20200622192900.22757-4-minchan@kernel.org>
 <CAK8P3a0Mnp2ekmX-BX9yr+N8fy2=gBtASELLXoa9uGSpSS9aOA@mail.gmail.com>
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On Fri, Aug 28, 2020 at 07:40:08PM +0200, Arnd Bergmann wrote:
> Every syscall that passes an iovec seems to do this. If we make import_iovec()
> handle both cases directly, this syscall and a number of others can
> be simplified, and you avoid the x32 entry point I mentioned above

FYI, I do have a series that does this (even tested) and kills tons of
compat syscalls by that.  But by doing that I found the problem that
compat syscalls issued by io_uring don't trigger in_compat_syscall().
I need to go back to fixing the io_uring vs in_compat_syscall() issue
(probably for 5.9) and then submit the whole thing.