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 814233A6F0B; Tue, 7 Apr 2026 10:13:11 +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=1775556793; cv=none; b=imHBGgRd5OvJcD7Higb9ZyiFYG88cGIBBUwim0YVlYRZ9QkVO4avyNXyccKAuhJpNSXq58xm3cXB5L2IL6CnaS2lp0fMs+QzLDuldUdICT1HA6Bp3ij6tZjJJVbCqdj8bGiW8TTt8GbOqCyCWGd0KwbtjSnRPibq3+jMfy+ehuE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775556793; c=relaxed/simple; bh=u6k7KReiIMT35ffIgZho6g6CodialPIJRfoN0WPK8T8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=oRU2Fl+kqHSEPKNICEaplD8HwL2SGR/9LtfrxwTGNvtqW4Se3/C42APaVIpMoBhfsz5QS48qC8CHnWNmfpDUOCvKSR57PDIGG+uTF95xM51n9EgfrwlmeTDYj/I4/qSYTXwkQtEs50Bh5Bu5ubXDHoT7OfqgecUt+rFZEPUoTu8= 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=BWNVh6AN; 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="BWNVh6AN" 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 2D5061BB2; Tue, 7 Apr 2026 03:13:05 -0700 (PDT) Received: from [10.57.87.42] (unknown [10.57.87.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3B2DD3F641; Tue, 7 Apr 2026 03:13:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1775556790; bh=u6k7KReiIMT35ffIgZho6g6CodialPIJRfoN0WPK8T8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=BWNVh6ANFtw0ueWu9yyum/s4AQLzADYVEGNe1bxpMRtjve3MThvdmz4uAY0F2iy4R 4PJrXK6QtuNLXqjAhnWeXyLIfgZSsfwLCKBML6k8kvo+BXcXRP0C3FTBqeV+daqvc2 bQkJZMH+IaAC4mVQ55h9T0x8Df47exrCEMB2Hmc4= Message-ID: Date: Tue, 7 Apr 2026 11:13:07 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] arm64: mm: Fix rodata=full block mapping support for realm guests Content-Language: en-GB To: Catalin Marinas Cc: Will Deacon , "David Hildenbrand (Arm)" , Dev Jain , Yang Shi , Suzuki K Poulose , Jinjiang Tu , Kevin Brodsky , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260330161705.3349825-1-ryan.roberts@arm.com> <20260330161705.3349825-2-ryan.roberts@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 07/04/2026 10:32, Catalin Marinas wrote: > On Tue, Apr 07, 2026 at 09:43:42AM +0100, Ryan Roberts wrote: >> On 03/04/2026 11:31, Catalin Marinas wrote: >>> On Thu, Apr 02, 2026 at 09:43:59PM +0100, Catalin Marinas wrote: >>>> Another thing I couldn't get my head around - IIUC is_realm_world() >>>> won't return true for map_mem() yet (if in a realm). Can we have realms >>>> on hardware that does not support BBML2_NOABORT? We may not have >>>> configuration with rodata_full set (it should be complementary to realm >>>> support). >>> >>> With rodata_full==false, can_set_direct_map() returns false initially >>> but after arm64_rsi_init() it starts returning true if is_realm_world(). >>> The side-effect is that map_mem() goes for block mappings and >>> linear_map_requires_bbml2 set to false. Later on, >>> linear_map_maybe_split_to_ptes() will skip the splitting. >>> >>> Unless I'm missing something, is_realm_world() calls in >>> force_pte_mapping() and can_set_direct_map() are useless. I'd remove >>> them and either require BBML2_NOABORT with CCA or get the user to force >>> rodata_full when running in realms. Or move arm64_rsi_init() even >>> earlier? >> >> I'd need Suzuki to comment on this. As I said in the other mail, I was treating >> this like a pre-existing bug. But I guess linear_map_requires_bbml2 ending up >> wrong is a problem here. I'm not sure it's quite as simple as requiring >> BBML2_NOABORT with CCA as we still need can_set_direct_map() to return true if >> we are in a realm. > > can_set_direct_map() == true is not a property of the realm but rather a > requirement. Yes indeed. It would be better to call it might_set_direct_map() or something like that... > In the absence of BBML2_NOABORT, I guess the test was added > under the assumption that force_pte_mapping() also returns true if > is_realm_world(). We might as well add a variable or static label to > track whether can_set_direct_map() is possible and avoid tests that > duplicate force_pte_mapping(). I'm not sure I follow. We have linear_map_requires_bbml2 which is inteded to track this shape of thing; if we have forced pte mapping then the value of can_set_direct_map() is irrelevant - we will never need to split because we are already pte-mapped. But if can_set_direct_map() initially returns false because is_realm_world() incorrectly returns false in the early boot environment, then linear_map_requires_bbml2 will be set to false, and we will incorrectly short-circuit splitting any block mappings in split_kernel_leaf_mapping(). I think we are agreed on the problem. But I don't understand how tracking can_set_direct_map() in a cached variable helps with that. > > This won't solve the is_realm_world() changing polarity during boot but > at least we know it won't suddenly make can_set_direct_map() return > true when it shouldn't. But is_real_world() _should_ make can_set_direct_map() return true, shouldn't it? If we are in realm-world, we need to be able to flip the NS_SHARED bit on parts of the linear map. So if we are in realm-world, we _might_ need to update he direct map and that's what can_set_direct_map() is supposed to tell us.