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[61.68.212.105]) by smtp.gmail.com with ESMTPSA id z126sm3602084pfc.94.2020.08.21.15.42.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Aug 2020 15:42:45 -0700 (PDT) Date: Sat, 22 Aug 2020 08:42:40 +1000 From: Nicholas Piggin Subject: Re: [PATCH v6 01/12] mm/vmalloc: fix vmalloc_to_page for huge vmap mappings To: Andrew Morton Cc: Christophe Leroy , Christoph Hellwig , Jonathan Cameron , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, Zefan Li References: <20200821151216.1005117-1-npiggin@gmail.com> <20200821151216.1005117-2-npiggin@gmail.com> <20200821130757.289570e4bb491672087d3396@linux-foundation.org> In-Reply-To: <20200821130757.289570e4bb491672087d3396@linux-foundation.org> MIME-Version: 1.0 Message-Id: <1598049375.u9pf1rciw6.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 77B5718229837 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Excerpts from Andrew Morton's message of August 22, 2020 6:07 am: > On Sat, 22 Aug 2020 01:12:05 +1000 Nicholas Piggin wr= ote: >=20 >> vmalloc_to_page returns NULL for addresses mapped by larger pages[*]. >> Whether or not a vmap is huge depends on the architecture details, >> alignments, boot options, etc., which the caller can not be expected >> to know. Therefore HUGE_VMAP is a regression for vmalloc_to_page. >=20 > I assume this doesn't matter in current mainline? > If wrong, then what are the user-visible effects and why no cc:stable? I haven't heard any reports, but in theory it could cause a prolem. The commit 029c54b095995 from the changelog was made to paper over it. But that was fixed properly afterward I think by 737326aa510b. Not sure of the user visible problems currently. I think generally you wouldn't do vmalloc_to_page() on ioremap() memory, so maybe callilng it a regression is a bit strong. _Technically_ a regression, maybe. Thanks, Nick