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Sat, 3 Mar 2018 18:12:03 -0500 Received: from mail-dm3nam03on0102.outbound.protection.outlook.com ([104.47.41.102]:24173 "EHLO NAM03-DM3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S935055AbeCCWjS (ORCPT ); Sat, 3 Mar 2018 17:39:18 -0500 From: Sasha Levin To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" CC: Anton Blanchard , Michael Ellerman , Sasha Levin Subject: [PATCH AUTOSEL for 4.4 050/115] powerpc: Avoid taking a data miss on every userspace instruction miss Thread-Topic: [PATCH AUTOSEL for 4.4 050/115] powerpc: Avoid taking a data miss on every userspace instruction miss Thread-Index: AQHTsz9YEJDimf73Wk6CXD+VNj0VAw== Date: Sat, 3 Mar 2018 22:31:17 +0000 Message-ID: <20180303223010.27106-50-alexander.levin@microsoft.com> References: <20180303223010.27106-1-alexander.levin@microsoft.com> In-Reply-To: <20180303223010.27106-1-alexander.levin@microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [52.168.54.252] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;MW2PR2101MB1113;7:XnfS/HmzZl67bRsSlCSh6RxbcD/OIlXJFUCWwfPToFrWddWYAJFL8GjUIz0z8sWJO+ETJvdhkE7QwObokS4iCv/pXfghJZ1A/DLdJ/ubuDTpXaavRSKAx25m5hXr7590wnN9jY4rtkfH8QOpjPnMY0o0Vfy2HQNxkAaXAodmFVPd8cuOUEyCF/913sbxL+4QshglNwG8N6hDg2E8Mm5o0wZpFj56qmPB34a/TxcZNnaWBv4retEml8K7+oUByNsj x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: f79783bb-0441-4474-20b3-08d5815798b0 x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(3008032)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603307)(7193020);SRVR:MW2PR2101MB1113; 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authentication-results: spf=none (sender IP is ) smtp.mailfrom=Alexander.Levin@microsoft.com; x-microsoft-antispam-message-info: BX0QTBmmxAfU6hj/ab1TClZfmosqrw/P2YVGpWfQ94PYMy0HPU1W8k+qjdIizlwVdkKnQCI9CvsKlHW9VdbBwuBfRsbuw/J+mBzHNjKa6jHG0QmSxQrwVQTRcI7MjvTjJCSHLvA5dzfFMRTCKHTGhStfuGgYcIbUu6WmRW2+luk= spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: f79783bb-0441-4474-20b3-08d5815798b0 X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Mar 2018 22:31:17.9165 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW2PR2101MB1113 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Anton Blanchard [ Upstream commit a7a9dcd882a67b68568868b988289fce5ffd8419 ] Early on in do_page_fault() we call store_updates_sp(), regardless of the type of exception. For an instruction miss this doesn't make sense, because we only use this information to detect if a data miss is the result of a stack expansion instruction or not. Worse still, it results in a data miss within every userspace instruction miss handler, because we try and load the very instruction we are about to install a pte for! A simple exec microbenchmark runs 6% faster on POWER8 with this fix: #include #include #include int main(int argc, char *argv[]) { unsigned long left =3D atol(argv[1]); char leftstr[16]; if (left-- =3D=3D 0) return 0; sprintf(leftstr, "%ld", left); execlp(argv[0], argv[0], leftstr, NULL); perror("exec failed\n"); return 0; } Pass the number of iterations on the command line (eg 10000) and time how long it takes to execute. Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman Signed-off-by: Sasha Levin --- arch/powerpc/mm/fault.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index a67c6d781c52..d154e333f76b 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -294,7 +294,7 @@ int __kprobes do_page_fault(struct pt_regs *regs, unsig= ned long address, * can result in fault, which will cause a deadlock when called with * mmap_sem held */ - if (user_mode(regs)) + if (!is_exec && user_mode(regs)) store_update_sp =3D store_updates_sp(regs); =20 if (user_mode(regs)) --=20 2.14.1