Re: [PATCH v4 3/6] mm/gup: remove vmas parameter from get_user_pages_remote()

From: Janosch Frank <frankja@linux.ibm.com>
To: Lorenzo Stoakes <lstoakes@gmail.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>,
	David Hildenbrand <david@redhat.com>,
	linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
	linux-s390@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-perf-users@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>,
	Eric Biederman <ebiederm@xmission.com>,
	Kees Cook <keescook@chromium.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
	Ian Rogers <irogers@google.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Kentaro Takeda <takedakn@nttdata.co.jp>,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	Paul Moore <paul@paul-moore.com>,
	James Morris <jmorris@namei.org>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v4 3/6] mm/gup: remove vmas parameter from get_user_pages_remote()
Date: Wed, 19 Apr 2023 14:05:26 +0200	[thread overview]
Message-ID: <ab586b59-7d62-2ea1-a617-ffbcf91f4037@linux.ibm.com> (raw)
In-Reply-To: <7c6f1ae88320bf11d2f583178a3d9e653e06ac63.1681831798.git.lstoakes@gmail.com>

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@arm.com> (for arm64)
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
> ---

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