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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 62A14C433EF for ; Thu, 13 Jan 2022 10:26:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=v6mnIdgQzEe0JFVnpHqo2O08bvzvP3BLWHrXnkxalTk=; b=RV2ajfwka9to3J RV1W1kH6e8wvbI/9aMmmLKhC8rsNC1iLnBlxklJAAqvl460zKRsWW016AmIvl+HqA0e/V/jgpw4F6 ItlQLzDnRAECxWznab0GoOSgfQLJ/gsxgW1ZGHH4l+9UQQDQScMAF1gZkc5VaTaqMKEH7kT2d9wVs ckLEQZ8U2cl4yTenFXiozRs7dMsrLLMz5TjfEpQ3XKKV8J1q0xpFIGJIyYdAFh5A8DLZID4DFQHXu D/jlTEdiGLuwJVaGXQU+KHT1ECAG023pbwiaT2r/8ZQO0L7EVJaj0eieBWSHRXbkkAmGlTCFL9oXn v/HYVItb0O+LWMhF7SrA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1n7xIG-005RID-Qu; Thu, 13 Jan 2022 10:25:20 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1n7xID-005RHS-Ds for linux-arm-kernel@lists.infradead.org; Thu, 13 Jan 2022 10:25:19 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 44A4D6D; Thu, 13 Jan 2022 02:25:15 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.5.145]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6468F3F766; Thu, 13 Jan 2022 02:25:14 -0800 (PST) Date: Thu, 13 Jan 2022 10:24:07 +0000 From: Mark Rutland To: Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, andre.przywara@arm.com, robin.murphy@arm.com Subject: Re: [bootwrapper PATCH] aarch64: Enable BRBE for the non-secure world Message-ID: References: <1642066868-23151-1-git-send-email-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1642066868-23151-1-git-send-email-anshuman.khandual@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220113_022517_541543_4943EA15 X-CRM114-Status: GOOD ( 19.52 ) 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 Hi Anshuman, This looks fine structurally, I'm just not sure of a couple of details because I can't find the relevant documentation -- more on that below. On Thu, Jan 13, 2022 at 03:11:08PM +0530, Anshuman Khandual wrote: > MDCR_EL3.SBRBE resets to an UNKNOWN value. Configure it to allow the BRBE > buffer usage and direct register access in the non-secure world. But just > before that, check AA64DFR0_EL1.BRBE and make sure BRBE is implemented. We > still continue to reset MDCR_EL3 register to zero with the exception of > MDCR_EL3.NSPB, MDCR_EL3.NSTB and MDCR_EL3.SBRBE. I'm struggling to find where the BRBE system register fields are documented. I looked at the latest ARM ARM (DDI 0487G.b): https://developer.arm.com/documentation/ddi0487/gb/ ... and the Armv9 supplement (DDI 0608A.a): https://developer.arm.com/documentation/ddi0608/aa/ ... but AFAICT, neither of those describe the bit-positions of the relevant fields, so I can't check that those are correct. The other extensions (at leat TME) describe that in the supplement, so this looks like a bug/oversight. Am I looking at the right documents? If this is meant to be in the supplement, could you please raise a bug report to get that fixed? > > Signed-off-by: Anshuman Khandual > --- > arch/aarch64/boot.S | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/aarch64/boot.S b/arch/aarch64/boot.S > index bfbb6ec..ca1b292 100644 > --- a/arch/aarch64/boot.S > +++ b/arch/aarch64/boot.S > @@ -103,6 +103,14 @@ ASM_FUNC(_start) > ldr x1, =(0x3 << 24) > orr x0, x0, x1 > > +1: mrs x1, id_aa64dfr0_el1 > + ubfx x1, x1, #52, #4 > + cbz x1, 1f > + > + // Enable BRBE for the non-secure world. > + ldr x1, =(0x3 << 32) > + orr x0, x0, x1 > + I assume this is the `SBRBE` field, which naming-wise sounds like it controls Secure rather than Non-Secure (e,g. by way of comparison to `NSPB`). Is that correct? What effect does the value 0x3 have? Thanks, Mark. > 1: msr mdcr_el3, x0 // Disable traps to EL3 > > mrs x0, id_aa64pfr0_el1 > -- > 2.7.4 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel