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=-8.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 052AEC433DF for ; Tue, 2 Jun 2020 05:29:09 +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 AB299206A2 for ; Tue, 2 Jun 2020 05:29:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB299206A2 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 bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 49bgZV4rVyzDqTL for ; Tue, 2 Jun 2020 15:29:06 +1000 (AEST) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 49bgVb2FktzDqRw for ; Tue, 2 Jun 2020 15:25:43 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix) id 49bgVZ4Rgbz9sSg; Tue, 2 Jun 2020 15:25:42 +1000 (AEST) Received: by ozlabs.org (Postfix, from userid 1034) id 49bgVZ3B6Mz9sSn; Tue, 2 Jun 2020 15:25:41 +1000 (AEST) X-powerpc-patch-notification: thanks X-powerpc-patch-commit: 595d153dd1022392083ac93a1550382cbee127e0 In-Reply-To: <20200526061808.2472279-1-mpe@ellerman.id.au> To: Michael Ellerman , linuxppc-dev@ozlabs.org From: Michael Ellerman Subject: Re: [PATCH] powerpc/64s: Fix restore of NV GPRs after facility unavailable exception Message-Id: <49bgVZ3B6Mz9sSn@ozlabs.org> Date: Tue, 2 Jun 2020 15:25:41 +1000 (AEST) 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: npiggin@gmail.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, 2020-05-26 at 06:18:08 UTC, Michael Ellerman wrote: > Commit 702f09805222 ("powerpc/64s/exception: Remove lite interrupt > return") changed the interrupt return path to not restore non-volatile > registers by default, and explicitly restore them in paths where it is > required. > > But it missed that the facility unavailable exception can sometimes > modify user registers, ie. when it does emulation of move from DSCR. > > This is seen as a failure of the dscr_sysfs_thread_test: > test: dscr_sysfs_thread_test > [cpu 0] User DSCR should be 1 but is 0 > failure: dscr_sysfs_thread_test > > So restore non-volatile GPRs after facility unavailable exceptions. > > Currently the hypervisor facility unavailable exception is also wired > up to call facility_unavailable_exception(). > > In practice we should never take a hypervisor facility unavailable > exception for the DSCR. On older bare metal systems we set HFSCR_DSCR > unconditionally in __init_HFSCR, or on newer systems it should be > enabled via the "data-stream-control-register" device tree CPU > feature. > > Even if it's not, since commit f3c99f97a3cd ("KVM: PPC: Book3S HV: > Don't access HFSCR, LPIDR or LPCR when running nested"), the KVM code > has unconditionally set HFSCR_DSCR when running guests. > > So we should only get a hypervisor facility unavailable for the DSCR > if skiboot has disabled the "data-stream-control-register" feature, > and we are somehow in guest context but not via KVM. > > Given all that, it should be unnecessary to add a restore of > non-volatile GPRs after the hypervisor facility exception, because we > never expect to hit that path. But equally we may as well add the > restore, because we never expect to hit that path, and if we ever did, > at least we would correctly restore the registers to their post > emulation state. > > In future we can split the non-HV and HV facility unavailable handling > so that there is no emulation in the HV handler, and then remove the > restore for the HV case. > > Fixes: 702f09805222 ("powerpc/64s/exception: Remove lite interrupt return") > Signed-off-by: Michael Ellerman Applied to powerpc fixes. https://git.kernel.org/powerpc/c/595d153dd1022392083ac93a1550382cbee127e0 cheers