From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 87EA022FE11 for ; Mon, 3 Mar 2025 19:39:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741030785; cv=none; b=PNMI13OAm3yVAxxEfxz7QugRpyYiXjRmFJhLLOyeFUDyIreY0beCR541f+3ocRJBaFzxtJef0+IdW+4o/W25QjMFE5zYO9ZW5h/gIL6wEYDWvuXCmab6TFkR+bnHFENjZYpKVyWC6TgY6WJjYv14DrPOhzWRjpXfGdx4Qp3mb9Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741030785; c=relaxed/simple; bh=M2WXSgM2HeFPnft4zW0yVlazq876TOaC1zHFap5xeGQ=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=CYNSB3QU0PADEzo4ZnJGHm28nuypEoE0i8JYL3rLQ2fs2hynRR+Bgi+WNX8JFo8QNN26dgDuKntg4JIw1+3Cm7R/MXnvuJRQq3uWUk4P4B5sBaqPhr/jgmdL/NldoMeHCXgVOvgTaLJ6eDoHSk+aieRd4gUuzwesre/mwNDMoFA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=W7Brfaxb; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="W7Brfaxb" 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) Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: 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 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.