From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C4902382295 for ; Thu, 30 Jul 2026 03:22:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785381764; cv=none; b=kOt85Kz1A9XLgiF50QWZ44XvHJ7X90UOn/80cgsZnSnrhIB5+cSdv80yyHe6PK6tVIyCXUrLgmtkr2ABLrtxHiruaBj6kvSc+c2hvtth2YTDSihnFyzrhar5JGwDKnjfUwcr4cGhfWwG9uhOLkTJFi/m07yeLq4Tnj7U+MPTBZI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785381764; c=relaxed/simple; bh=/1yTzYFGg3pV1usAbAUtPbtP+HA7uKNwPQmps+iLHVA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XCcNXAWNKYXIO7dn+PBos1/rX7SiFRksdWJ+9T1faP+zKBWCDKzd6Tgyi8zkXPyvf2UW/1/8pbHpQthbLOtEpoKieFOYUmOkiCtsAcfyZQdMU6WHqSVSex+Luyf4Qaz1PSRExxb8Kp7oZBer3hhEEFa9PHgl/b8Lod5c5G5yrtc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=WC5qUcaN; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="WC5qUcaN" 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 E7E891684; Wed, 29 Jul 2026 20:22:36 -0700 (PDT) Received: from localhost (a079125.arm.com [10.164.21.43]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 451723F763; Wed, 29 Jul 2026 20:22:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1785381761; bh=/1yTzYFGg3pV1usAbAUtPbtP+HA7uKNwPQmps+iLHVA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=WC5qUcaNXp7YRQUQva+KqAzlEwiNFkhj7vRPDnylSaQJ9cC9iMAcGpdkb6rq9cNiF /OjqhnNkYflxnuK1FVgGTmKpcdsMQAvdg00NrAI4KnmgAfYsOjtXjolU8Rma8WQzmS BYW4vmCoGUyIU7evJ61g8aN7ThcGiL3Myb5xUHL4= Date: Thu, 30 Jul 2026 08:52:37 +0530 From: Linu Cherian To: Mostafa Saleh Cc: linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, maz@kernel.org, oupton@kernel.org, seiden@linux.ibm.com, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, vdonnefort@google.com, tabba@google.com, sebastianene@google.com, keirf@google.com Subject: Re: [RFC PATCH v2 0/2] KVM: arm64: Add support for BBM level 3 Message-ID: References: <20260723182140.4025575-1-smostafa@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260723182140.4025575-1-smostafa@google.com> Hi, On Thu, Jul 23, 2026 at 06:21:38PM +0000, Mostafa Saleh wrote: > This patch series adds support for BBM level 3 to KVM pgtable, it > depends on [1] > > Changes from v1: > https://lore.kernel.org/all/20260717130901.2239134-1-smostafa@google.com/ > - Limit BBML3 to systems with FWB and DIC and remove race check. > > Motivation > ========== > I have been looking into this for the context of: > - Page table sharing between the host CPU stage-2 and the SMMUv3 for > protected KVM. > - Use the pagtable code to populate SMMUv3 stage-2 shadowed > page table [2] > > However, BBM level 3 is still useful for CPU only operations as it > avoids intermediately breaking translation. > > Design > ====== > Some of the conditions that BBM level 3 will be useful in (RWHZWS): > 1) A change to a PTE memory type, shareability, cacheability or OA Could you please clarify how BBM level 3 is helping this particular scenario ? This is supposed to be a case where break before make is required. Thanks, Linu Cherian.