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 A1703C4345F for ; Wed, 1 May 2024 17:57:42 +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=r2irMVp/idhaX1/ieRi9ce35BEzlDRf4IibzQzsNPAc=; b=JuW7aZAyw2EIii q9TUESKmWGBgqbFizWcbH7H0ZADWLIRK+5VZtXu/I/nlZ5Ydy5Br0IEAE9WsfQ6N82c4kQRFq9/sj d2tvxjxgtXaeR+4khV1TXtOEoEELB5HTuucn8L+zpu/1CCJj9lVklFeHrbxDfaF1jn47VDa2VTrHm TNkxqu9tilJAk09CPcinFI3OTybKAz1df7/4nLlh3h+iik1b37Gv037tBDD76smiN28CkhroYbW6G puvwAwFNfPgzVwNSjLPNMfJS+/wt1yQLBMsyqBsh4Fc+KhRid2aursP3Rqpxp5ue/INx5DaJOMH6D AO+FTdhRuM/7GIn2+F9g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1s2ECx-0000000AMoO-0syk; Wed, 01 May 2024 17:57:31 +0000 Received: from out-189.mta1.migadu.com ([95.215.58.189]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1s2ECt-0000000AMns-4BK7 for linux-arm-kernel@lists.infradead.org; Wed, 01 May 2024 17:57:29 +0000 Date: Wed, 1 May 2024 17:57:20 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1714586244; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Tt/PxbcUEf64em4t5RxtHA8scveQfLCnFNCRhqS43k4=; b=g2wJOg3xD+QENajCvslA7fX7MOIbIQkbx222rTDT80vlbwYnEHFKTTX4vWQEViXh+WRt1m sm2eUu+eeD7JGslpjvNFgc2iqWTdvnhu0EmGdZQGNK9/sZnWYifvX9U9EFHWhjDJV+oJT6 dvAWNhyvSMRL9Nr7Io7liA6YiWUd+vg= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: "Russell King (Oracle)" Cc: Marc Zyngier , Catalin Marinas , Will Deacon , James Morse , Suzuki K Poulose , Zenghui Yu , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev Subject: Re: [PATCH RFC] KVM: arm64: allow ID_MMFR4_EL1 to be writable Message-ID: References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240501_105728_346200_0D866597 X-CRM114-Status: GOOD ( 14.08 ) 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 Russell, On Wed, May 01, 2024 at 06:06:51PM +0100, Russell King (Oracle) wrote: > Between 5.4 and 5.15, the guests view of HPDS, CnP, XNX and AC2 > changed their value on the same Neoverse N1 r3p1 hardware which makes > migrating between these kernels on the host problematical. It'd be helpful to expand a bit more on how these fields changed, better yet if we can blame it back to a commit. I'm guessing the only direction of migration you care about is old -> new then? > We already permit changing HPDS in AA64MMFR1_EL1 and CnP in > AA64MMFR2_EL1. We also allow LSM as we allow that in AA64MMFR2_EL1, > so this patch includes support for that even though it isn't required. > > Discussing with Marc Zygnier, AC2 should also be fine to be writable, typo: Zyngier > even though we don't inject an UNDEF if the guest accesses those > registers. > > The only questionable one is XNX, execute-never control distinction, > which is also in AA64MMFR1_EL1 but we don't allow to be changed there. It is quite odd for us to expose this field to non-nested VMs in the first place, though I suppose we will apply an additional set of restrictions for nested VMs when they come along. -- Thanks, Oliver _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel