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Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1rVwp2-0048AR-0P; Fri, 02 Feb 2024 16:55:24 +0000 Date: Fri, 2 Feb 2024 16:55:24 +0000 From: Al Viro To: Doug Anderson Cc: Christian Brauner , Eric Biederman , Jan Kara , Kees Cook , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Oleg Nesterov , Catalin Marinas , Will Deacon , Linux ARM Subject: Re: [PATCH] regset: use vmalloc() for regset_get_alloc() Message-ID: <20240202165524.GD2087318@ZenIV> References: <20240201171159.1.Id9ad163b60d21c9e56c2d686b0cc9083a8ba7924@changeid> <20240202012249.GU2087318@ZenIV> <20240202030438.GV2087318@ZenIV> <20240202034925.GW2087318@ZenIV> <20240202040503.GX2087318@ZenIV> <20240202164947.GC2087318@ZenIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240202164947.GC2087318@ZenIV> X-Rspam-User: X-Stat-Signature: cdfdk5kixrxb3yuzdpeqkx1ow6dmdtxx X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 9BCC318000B X-HE-Tag: 1706892936-552159 X-HE-Meta: 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 tablKAFe GqIpbp1WUexfFRBkUEmqiZ/5M46MNewDPjvj+eI2smTdZReR2kf8UGfE26ZA7qz3nenVjdvLM651KY/a6j8vvRZpBaP8r8WROxPiJOf1QhaE8E7SS4fEwft8VZm+mglg9O0s+rO2bj0pFH8SbD/322ci85IAJFyTfMRBpUqHKmhRIippMxwLnPfBAz6r2DjlghFT+GpBm60yGbXyfX6RGKyEs7YGADtK/DpA5OShpO5T1Hpqy/OQxx8PEGDZikY8ZW/1Jg8n6T52HDso9+10I+JOBabmb6w3OUTUc4hilDElYmwHkFgerlEPE3Tf8Tyx4f74Q/oymG38rnLb1/gxuzeJe9Db0UqXY/0NP7hVWZL834H1yy3c5YCTxfsTn2WbzM8iqUoPoTFcm11+7FY5nqb5F7g== 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: List-Subscribe: List-Unsubscribe: On Fri, Feb 02, 2024 at 04:49:47PM +0000, Al Viro wrote: > > +folks from `./scripts/get_maintainer.pl -f arch/arm64/kernel/ptrace.c` > > > > Trying to follow the macros to see where "n" comes from is a maze of > > twisty little passages, all alike. Hopefully someone from the ARM > > world can help tell if the value of 17474 for n here is correct or if > > something is wonky. > > It might be interesting to have it print the return value of __regset_get() > in those cases; if *that* is huge, we really have a problem. If it ends up > small enough to fit into few pages, OTOH... > > SVE_VQ_MAX is defined as 255; is that really in units of 128 bits? IOW, > do we really expect to support 32Kbit registers? That would drive the > size into that range, all right, but it would really suck on context > switches. > > I could be misreading it, though - the macros in there are not easy to > follow and I've never dealt with SVE before, so take the above with > a cartload of salt. Worse - it's SVE_VQ_MAX is 512; sorry about the confusion. OK, that would certainly explain the size (header + 32 registers, each up to 512 * 16 bytes), but... ouch.