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Fri, 13 Aug 2021 17:41:35 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mEbBR-00DHbD-Jr for linux-arm-kernel@lists.infradead.org; Fri, 13 Aug 2021 17:41:33 +0000 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 3241D60F51; Fri, 13 Aug 2021 17:41:29 +0000 (UTC) Received: from 109-170-232-56.xdsl.murphx.net ([109.170.232.56] helo=wait-a-minute.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 1mEbBP-004qe7-2x; Fri, 13 Aug 2021 18:41:27 +0100 Date: Fri, 13 Aug 2021 18:41:36 +0100 Message-ID: <87im091bu7.wl-maz@kernel.org> From: Marc Zyngier To: Robin Murphy Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= , Will Deacon , Catalin Marinas , Mark Rutland , Ard Biesheuvel , Florian Fainelli , bcm-kernel-feedback-list@broadcom.com, kernel-team@android.com Subject: Re: [PATCH 2/5] arm64: Handle UNDEF in the EL2 stub vectors In-Reply-To: <2f6bf17f-d235-8311-13d5-dcb3d00e23c4@arm.com> References: <20210812190213.2601506-1-maz@kernel.org> <20210812190213.2601506-3-maz@kernel.org> <2f6bf17f-d235-8311-13d5-dcb3d00e23c4@arm.com> 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") X-SA-Exim-Connect-IP: 109.170.232.56 X-SA-Exim-Rcpt-To: robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, zajec5@gmail.com, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, ardb@kernel.org, f.fainelli@gmail.com, bcm-kernel-feedback-list@broadcom.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210813_104129_727230_A5E19B29 X-CRM114-Status: GOOD ( 30.79 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 13 Aug 2021 14:08:23 +0100, Robin Murphy wrote: > > On 2021-08-12 20:02, Marc Zyngier wrote: > > As we want to handle the silly case where HVC has been disabled > > from EL3, augment our ability to handle exception at EL2. > > > > Check for unknown exceptions (usually UNDEF) coming from EL2, > > and treat them as a failing HVC call into the stubs. While > > this isn't great and obviously doesn't catter for the gigantic > > range of possible exceptions, it isn't any worse than what we > > have today. > > > > Just don't try and use it for anything else. > > > > Signed-off-by: Marc Zyngier > > --- > > arch/arm64/kernel/hyp-stub.S | 19 ++++++++++++++++++- > > 1 file changed, 18 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S > > index 43d212618834..026a34515b21 100644 > > --- a/arch/arm64/kernel/hyp-stub.S > > +++ b/arch/arm64/kernel/hyp-stub.S > > @@ -46,7 +46,16 @@ SYM_CODE_END(__hyp_stub_vectors) > > .align 11 > > SYM_CODE_START_LOCAL(elx_sync) > > - cmp x0, #HVC_SET_VECTORS > > + mrs x4, spsr_el2 > > + and x4, x4, #PSR_MODE_MASK > > + orr x4, x4, #1 > > + cmp x4, #PSR_MODE_EL2h > > + b.ne 0f > > + mrs x4, esr_el2 > > + eor x4, x4, #ESR_ELx_IL > > + cbz x4, el2_undef > > Hmm, might it be neater to check ESR_EL2.ISS to see if we landed here > for any reason *other* than a successfully-executed HVC? We absolutely could. However, the sixpence question (yes, that's the Brexit effect for you) is "what do you do with exceptions that are neither UNDEF now HVC?". We are taking a leap of faith by assuming that the only thing that will UNDEF at EL2 while the stubs are installed is HVC. If anything else occurs, I have no idea what to do with it. I guess we could always ignore it instead of treating it as a HVC (as it is done at the moment). Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel