linux-kernel - Re: [PATCH v4 3/6] mm/gup: remove vmas parameter from get_user_pages

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Date:   Wed, 19 Apr 2023 14:05:26 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kentaro Takeda <takedakn@...data.co.jp>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v4 3/6] mm/gup: remove vmas parameter from
 get_user_pages_remote()

On 4/18/23 17:49, Lorenzo Stoakes wrote:
> The only instances of get_user_pages_remote() invocations which used the
> vmas parameter were for a single page which can instead simply look up the
> VMA directly. In particular:-
> 
> - __update_ref_ctr() looked up the VMA but did nothing with it so we simply
>    remove it.
> 
> - __access_remote_vm() was already using vma_lookup() when the original
>    lookup failed so by doing the lookup directly this also de-duplicates the
>    code.
> 
> We are able to perform these VMA operations as we already hold the
> mmap_lock in order to be able to call get_user_pages_remote().
> 
> As part of this work we add get_user_page_vma_remote() which abstracts the
> VMA lookup, error handling and decrementing the page reference count should
> the VMA lookup fail.
> 
> This forms part of a broader set of patches intended to eliminate the vmas
> parameter altogether.
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@....com> (for arm64)
> Acked-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
> ---

For the s390 part:
Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>