From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EF7C5C43381 for ; Thu, 28 Feb 2019 09:32:18 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 78F172171F for ; Thu, 28 Feb 2019 09:32:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 78F172171F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4496lN2pHzzDq8v for ; Thu, 28 Feb 2019 20:32:16 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4496Vd3FnbzDqGv for ; Thu, 28 Feb 2019 20:21:13 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix, from userid 1034) id 4496Vd1f7xz9sBF; Thu, 28 Feb 2019 20:21:12 +1100 (AEDT) X-powerpc-patch-notification: thanks X-powerpc-patch-commit: 75d9fc7fd94eb43cdf0bec04499a27ced780af19 X-Patchwork-Hint: ignore In-Reply-To: <20190226093035.7176-1-npiggin@gmail.com> To: Nicholas Piggin , linuxppc-dev@lists.ozlabs.org From: Michael Ellerman Subject: Re: powerpc/powernv: move OPAL call wrapper tracing and interrupt handling to C Message-Id: <4496Vd1f7xz9sBF@ozlabs.org> Date: Thu, 28 Feb 2019 20:21:12 +1100 (AEDT) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Nicholas Piggin Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, 2019-02-26 at 09:30:35 UTC, Nicholas Piggin wrote: > The OPAL call wrapper gets interrupt disabling wrong. It disables > interrupts just by clearing MSR[EE], which has two problems: > > - It doesn't call into the IRQ tracing subsystem, which means tracing > across OPAL calls does not always notice IRQs have been disabled. > > - It doesn't go through the IRQ soft-mask code, which causes a minor > bug. MSR[EE] can not be restored by saving the MSR then clearing > MSR[EE], because a racing interrupt while soft-masked could clear > MSR[EE] between the two steps. This can cause MSR[EE] to be > incorrectly enabled when the OPAL call returns. Fortunately that > should only result in another masked interrupt being taken to > disable MSR[EE] again, but it's a bit sloppy. > > The existing code also saves MSR to PACA, which is not re-entrant if > there is a nested OPAL call from different MSR contexts, which can > happen these days with SRESET interrupts on bare metal. > > To fix these issues, move the tracing and IRQ handling code to C, and > call into asm just for the low level call when everything is ready to > go. Save the MSR on stack rather than PACA. > > Performance cost is kept to a minimum with a few optimisations: > > - The endian switch upon return is combined with the MSR restore, > which avoids an expensive context synchronizing operation for LE > kernels. This makes up for the additional mtmsrd to enable > interrupts with local_irq_enable(). > > - blr is now used to return from the opal_* functions that are called > as C functions, to avoid link stack corruption. This requires a > skiboot fix as well to keep the call stack balanced. > > A NULL call is more costly after this, (410ns->430ns on POWER9), but > OPAL calls are generally not performance critical at this scale. > > Signed-off-by: Nicholas Piggin Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/75d9fc7fd94eb43cdf0bec04499a27ce cheers