From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751768AbaHKLyv (ORCPT ); Mon, 11 Aug 2014 07:54:51 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:45497 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751196AbaHKLyu (ORCPT ); Mon, 11 Aug 2014 07:54:50 -0400 Date: Mon, 11 Aug 2014 13:54:31 +0200 From: Peter Zijlstra To: "Sha, Ruibin" Cc: Chintan Pandya , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "mel@csn.ul.ie" , "mgorman@suse.de" , "mingo@redhat.com" , "Zhang, Yanmin" , "He, Bo" Subject: Re: [PATCH] export the function kmap_flush_unused. Message-ID: <20140811115431.GW9918@twins.programming.kicks-ass.net> References: <3C85A229999D6B4A89FA64D4680BA6142C7DFA@SHSMSX101.ccr.corp.intel.com> <53E4D312.5000601@codeaurora.org> <3C85A229999D6B4A89FA64D4680BA6142CAFF3@SHSMSX101.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="PPU/y5W3JEc6wR1b" Content-Disposition: inline In-Reply-To: <3C85A229999D6B4A89FA64D4680BA6142CAFF3@SHSMSX101.ccr.corp.intel.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --PPU/y5W3JEc6wR1b Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Aug 11, 2014 at 01:26:45AM +0000, Sha, Ruibin wrote: > Hi Chintan, > Thank you very much for your timely and kindly response and comments. >=20 > Here is more detail about our Scenario: >=20 > We have a big driver on Android product. The driver allocates lots of > DDR pages. When applications mmap a file exported from the driver, > driver would mmap the pages to the application space, usually with > uncachable prot. > On ia32/x86_64 arch, we have to avoid page cache alias issue. When > driver allocates the pages, it would change page original mapping in > page table with uncachable prot. Sometimes, the allocated page was > used by kmap/kunmap. After kunmap, the page is still mapped in KMAP > space. The entries in KMAP page table are not cleaned up until a > kernel thread flushes the freed KMAP pages(usually it is woken up by = kunmap). > It means the driver need force to flush the KMAP page table entries = before mapping pages to > application space to be used. Otherwise, there is a race to create > cache alias. >=20 > To resolve this issue, we need export function kmap_flush_unused as > the driver is compiled as module. Then, the driver calls > kmap_flush_unused if the allocated pages are in HIGHMEM and being > used by kmap. A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail? That said, it sounds like you want set_memory_() to call kmap_flush_unused(). Because this race it not at all specific to your usage, it could happen to any set_memory_() site, right? --PPU/y5W3JEc6wR1b Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJT6K7yAAoJEHZH4aRLwOS684sQAK4J9mCnVRUMUPR7DHtyfh0m jv8U6nSsXIQ5pY454Z/zxXMnhWTKqFJ5e+QzRdgTZC24pg4dj1qzQImXcdjwuPTN 3gUlDoajSU2IXT3JODFtSfKm/weylsWaObzn6ou7t3FboPLhfymrAdR0nkbO+bxh Vpz9SPnAMQqPXeTbLzbPUfB0udtUzudFkk85tP+okGpj13uqvfTpEqX0EnaIk9hS Zb9t+W49z3e4T9B6NWuA2PBhVWMRKrpGAdKq9/OqkFierwLKkt1UFLuP84VUedwZ haEKlLlp6mT/DfP8v62cGXOSZrDTDxm9fSeZVhPUlNzwpSXcJg+BNWrpW58wLs1g mNHIBe/a+tRwqZ2WwSkDD5kJWHAhqkbeOfzt6+lmRh/bZinwm7urpW/KDMZcnvGV S8qKXNhY2I0mzKzkxok1vB7GRP/OLjjauRfNk7WxVJNV++gq7AcyQYzNhzWPhKw7 hpx+Y7NEqnHPHbBirq0jqrv8GeNuZCfwWZfi60M3d3K62Zx14rpDkySiCdMNpJq5 ebPGpa49VAaxhzpR7Tr2aIltDet5C3rJOioQp4qrUjvpkbdCYvoxzxgD1AIDZNvX 7cp+dbYsT3f242Nl0uGgxznsrcr6e6lhzEFkmLm9mVSI6NjClJs/OA8EJ3VELKSo TwQfCfSE2FOWWezBk0jR =vCVR -----END PGP SIGNATURE----- --PPU/y5W3JEc6wR1b--