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 04E5BC282C6 for ; Mon, 3 Mar 2025 19:41:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: References:In-Reply-To:Subject:Cc:To:From:Message-ID:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=EZ6A/fJznSTv8KroRQXgduiuIC3GojwxicoK7Ugll1c=; b=mLgoy2jhudmPbwvE8y1gy+mHIg z9BP6fM69IWnFPT3qVqDVYWehL9tblbHqyaewDYQOVpBM/25uWmlLf7w9vdujKy9K8Nd3OogXs8eE 8HIFvku3DBNM3AiXy1FkwfyaoUsYriD64Hn0QMt4pCO1qkWUmjOdEct8Ro+XstcbKSpEt+MljO04x 9hAZw/NdITXORayWFgO6rVODGG219SJPWGRiUH2baH0I+DtafFf2yewFrjSN+Zvs23Q4i3dtkHOJi rcFBSBlMB4eZijgIO+lN1+CFSfhmVHZ69f3ZgWmj2KmwFTgVJCkbsju7XrWzEgpekP0K0UGCkwQkA c0ft4ZQA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tpBfE-000000025aY-3Tci; Mon, 03 Mar 2025 19:41:20 +0000 Received: from nyc.source.kernel.org ([147.75.193.91]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tpBdg-000000025TC-09C8 for linux-arm-kernel@lists.infradead.org; Mon, 03 Mar 2025 19:39:45 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id 4CC3CA44CF6; Mon, 3 Mar 2025 19:34:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E0C77C4CED6; Mon, 3 Mar 2025 19:39:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1741030782; bh=M2WXSgM2HeFPnft4zW0yVlazq876TOaC1zHFap5xeGQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=W7Brfaxb6JOcZob72taN81B+Ju69SlvivSSxJUsmPLrU2qhsTiXvOO8HFPL5T5ycs aVYC2dcQH1vAmdt14kYfnKg/mWmVorSfYuAod/B+XwEbD87nrlYmkSuz4gc3Hb+pj+ sEtQbYkW8nKL4E+S6TT5Mdk/Nf+2WYnDhdHuydn23rcQwQKwM7WE9GBfGtv+K++Fm5 9HKUQB8EI1s7d78+Tala6CgC2wYpLbz8y/T7aIEeUKYnZhzW+okf1ilXZ3NRjtuONd af4Vh+iZe1LpPdG1ZTzCJjmzOF5Ot2tD5Tc4e4LtdAA9bnRMI+ejOzLvZ+DjNUOkD+ QcuZfAweyW/Fg== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1tpBdc-009y7I-LD; Mon, 03 Mar 2025 19:39:40 +0000 Date: Mon, 03 Mar 2025 19:39:40 +0000 Message-ID: <86h649q4xv.wl-maz@kernel.org> From: Marc Zyngier To: Sebastian Ott Cc: Oliver Upton , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev Subject: Re: writable ID_AA64MMFR0_EL1.TGRAN*_2 ? In-Reply-To: <597411b1-ff60-edc3-d6f2-1b21ce2e34e9@redhat.com> References: <597411b1-ff60-edc3-d6f2-1b21ce2e34e9@redhat.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/29.4 (aarch64-unknown-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: 185.219.108.64 X-SA-Exim-Rcpt-To: sebott@redhat.com, oliver.upton@linux.dev, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev 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-20250303_113944_137441_04F05287 X-CRM114-Status: GOOD ( 15.76 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 28 Feb 2025 15:19:06 +0000, Sebastian Ott wrote: > > Hi, > > I'm looking into the possibility of migrating between 2 (Graviton) hosts > and the only ID register diffs that are not yet writable are TGRAN*_2. > Both hosts support the same sizes for S2 but express that differently > (2==supported vs 0=="look at TGRAN*"). > > One idea would be to either set the guest view for these to NI (for the > "normal" / not nested guest) or allow to convert between the 2 values > (and maybe also allow to write NI for good measure). I think we can allow any value to be written to any of the TGRAN*_2 in a non-NV context. For NV, we must be fairly strict, by enforcing that NI is the floor limit for the feature (we cannot let 0 be written for any of them). Thanks, M. -- Without deviation from the norm, progress is not possible.