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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,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 02F81C47080 for ; Tue, 1 Jun 2021 12:23:04 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8AE0160FF0 for ; Tue, 1 Jun 2021 12:23:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8AE0160FF0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1E4106B00C7; Tue, 1 Jun 2021 08:23:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 194A26B00C8; Tue, 1 Jun 2021 08:23:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 00D2B6B00C9; Tue, 1 Jun 2021 08:23:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0157.hostedemail.com [216.40.44.157]) by kanga.kvack.org (Postfix) with ESMTP id B886E6B00C7 for ; Tue, 1 Jun 2021 08:23:02 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 566168249980 for ; Tue, 1 Jun 2021 12:23:02 +0000 (UTC) X-FDA: 78205069404.21.3E3A956 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf20.hostedemail.com (Postfix) with ESMTP id BF3E0543 for ; Tue, 1 Jun 2021 12:22:45 +0000 (UTC) Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E9693613AD; Tue, 1 Jun 2021 12:23:00 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lo3QA-004oP5-RK; Tue, 01 Jun 2021 13:22:58 +0100 Date: Tue, 01 Jun 2021 13:22:57 +0100 Message-ID: <87r1hl22qm.wl-maz@kernel.org> From: Marc Zyngier To: Pavel Tatashin Cc: James Morris , Sasha Levin , "Eric W. Biederman" , kexec mailing list , LKML , Jonathan Corbet , Catalin Marinas , Will Deacon , Linux ARM , James Morse , Vladimir Murzin , Matthias Brugger , linux-mm , Mark Rutland , steve.capper@arm.com, rfontana@redhat.com, Thomas Gleixner , Selin Dag , Tyler Hicks , Pingfan Liu , Andrew Morton , madvenka@linux.microsoft.com Subject: Re: [PATCH 03/18] arm64: hyp-stub: Move elx_sync into the vectors In-Reply-To: References: <20210527150526.271941-1-pasha.tatashin@soleen.com> <20210527150526.271941-4-pasha.tatashin@soleen.com> <87sg28rx3c.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: pasha.tatashin@soleen.com, jmorris@namei.org, sashal@kernel.org, ebiederm@xmission.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, corbet@lwn.net, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, james.morse@arm.com, vladimir.murzin@arm.com, matthias.bgg@gmail.com, linux-mm@kvack.org, mark.rutland@arm.com, steve.capper@arm.com, rfontana@redhat.com, tglx@linutronix.de, selindag@gmail.com, tyhicks@linux.microsoft.com, kernelfans@gmail.com, akpm@linux-foundation.org, madvenka@linux.microsoft.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-Rspamd-Queue-Id: BF3E0543 Authentication-Results: imf20.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf20.hostedemail.com: domain of maz@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=maz@kernel.org X-Rspamd-Server: rspam04 X-Stat-Signature: x55x17t8xodpxe8rqog3x8sz4akzt3m8 X-HE-Tag: 1622550165-886206 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: On Thu, 27 May 2021 22:23:22 +0100, Pavel Tatashin wrote: > > On Thu, May 27, 2021 at 11:54 AM Marc Zyngier wrote: > > > > On Thu, 27 May 2021 16:05:11 +0100, > > Pavel Tatashin wrote: > > > > > > The hyp-stub's elx_sync code fits in the vector. > > > > > > With this, all of the hyp-stubs behaviour is contained in its vectors. > > > This lets kexec and hibernate copy the hyp-stub when they need its > > > behaviour, instead of re-implementing it. > > > > > > Co-developed-by: James Morse > > > Signed-off-by: Pavel Tatashin > > > --- > > > arch/arm64/kernel/hyp-stub.S | 64 +++++++++++++++++++----------------- > > > 1 file changed, 33 insertions(+), 31 deletions(-) > > > > > > diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S > > > index 18a97bee3779..86af6c4e52b9 100644 > > > --- a/arch/arm64/kernel/hyp-stub.S > > > +++ b/arch/arm64/kernel/hyp-stub.S > > > @@ -21,6 +21,37 @@ SYM_CODE_START_LOCAL(\label) > > > .align 7 > > > b \label > > > SYM_CODE_END(\label) > > > +.endm > > > + > > > +.macro elx_sync_vector label > > > +SYM_CODE_START_LOCAL(\label) > > > + .align 7 > > > + cmp x0, #HVC_SET_VECTORS > > > + b.ne 1f > > > + msr vbar_el2, x1 > > > + b 9f > > > + > > > +1: cmp x0, #HVC_VHE_RESTART > > > + b.eq mutate_to_vhe > > > > Now that this has turned into a macro, what are the guarantees that > > mutate_to_vhe will be within reach of the site where this macro is > > expanded? It does work here, but what about the other expansion sites > > that will show up later in the series? > > > > What was wrong with directly branching to the original call site? > > Nothing in the commit message explains it. > > Hi Marc, > > I need to explain this better in the commit log. Later in the series > we create our own vector copy that is outside of the old and new > kernel so it does not get overwritten during kexec relocation. When > VHE is enabled, the vector is passed so we can switch to el2 before > jumping to the new kernel. > > arm64_relocate_new_kernel() which performs the relocation runs with > MMU being enabled until relocation is done, after that disables MMU > and if vectors are passed performs: > > mov x0, #HVC_SOFT_RESTART > hvc #0 /* Jumps from el2 */ > > It cannot call mutate_to_vhe because #HVC_VHE_RESTART is not used > here. But, if it had to it would not work as we cannot return to the > old kernel text after relocation. OK, so you are happy with having a dangling branch pointing to nowhere? Something in me screams that it isn't a good idea, in general. If HVC_SOFT_RESTART is all you need, I'd rather you have a small stub that implements exactly that and nothing else. Feel free to extract it as a reusable macro if you want. Thanks, M. -- Without deviation from the norm, progress is not possible.