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 BA1F93B52E1; Wed, 7 Oct 2026 11:13:31 +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=1791371628; cv=none; b=d7TKcTQZlIiI8uLT4Y3lz1F2pZ6ShBq61CoWajD9BjUTyGNlhmFtDNVGKHOQUupXebzn/ReWZGQCCeEDahNXQcCwTbVkoh1xqhhFIXRF/v4WHXRfbpFa93TZZBS5Y/rwqyu+r9Ke4Ahsorl24AuDqx58sbZMeIKiGaoVnXsOXNc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791371628; c=relaxed/simple; bh=XkPVGrUWVDU6Wer3sPwtuoNfUx3GZi0QoXy/izLzVhE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dIDAmcftOY3TMw7RoivFBo8+AZYH66er/uaB+PfDd0pRAfo45mpKZVBkcbgH+OXMZd5h4p+jATl5gb4ZJE0uMZHAh6abT+jNWDFqeoVzwVflvyu86bgHIwh3nadQAaWtfHPNhj3UYFJzMK5n8F5eTNW/WEF5iUMIOe1UZ8/qp7U= 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=igUveoCg; 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="igUveoCg" 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 753031595; Wed, 7 Oct 2026 04:13:27 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 582333F66F; Wed, 7 Oct 2026 04:13:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1791371610; bh=XkPVGrUWVDU6Wer3sPwtuoNfUx3GZi0QoXy/izLzVhE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=igUveoCg91F1QZl6TCWGQXum8trlGIS+yJnnGXsR+anmFKmTZ1B9TBQsyFhsbvTr3 8LWHLfx0Csp/j+Uam2n55lceRPr9TQ6wTKf+Lwm9q7pLVb3aBVKndMODvi3zPKvm0V t+PIIdBd0ff3Gzs8GCEjofEnDKdb1Cf+a6Zffw4w= Date: Wed, 7 Oct 2026 12:13:20 +0100 From: Catalin Marinas To: Will Deacon Cc: "Aneesh Kumar K.V (Arm)" , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Robin Murphy , Marek Szyprowski , Jonathan Corbet , Shuah Khan , Randy Dunlap , Mark Rutland , Marc Zyngier , Steven Price , Suzuki K Poulose , Jiri Pirko , Jason Gunthorpe , Mostafa Saleh , Petr Tesarik , Alexey Kardashevskiy , Dan Williams , Xu Yilun , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , "Ritesh Harjani (IBM)" , Shrikanth Hegde , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Stefano Stabellini , Russell King , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , Jiaxun Yang , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH v6 6/8] dma: swiotlb: Centralize memory-encryption pool sizing Message-ID: References: <20260924060756.1325156-1-aneesh.kumar@kernel.org> <20260924060756.1325156-7-aneesh.kumar@kernel.org> 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: On Wed, Oct 07, 2026 at 11:43:06AM +0100, Will Deacon wrote: > On Wed, Oct 07, 2026 at 11:04:05AM +0100, Catalin Marinas wrote: > > On Tue, Oct 06, 2026 at 10:49:17PM +0100, Will Deacon wrote: > > > On Thu, Sep 24, 2026 at 11:37:54AM +0530, Aneesh Kumar K.V (Arm) wrote: > > > > @@ -496,7 +516,8 @@ swiotlb_select_pool_policy(unsigned int flags) > > > > if (swiotlb_force_disable) > > > > return SWIOTLB_POOL_NONE; > > > > > > > > - if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) > > > > + if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) && > > > > + !restricted_dma_pool_present) > > > > return SWIOTLB_POOL_CC_GUEST; > > > > > > I think this check on the restricted DMA pool is too general -- the pool > > > could be tied to a specific DMA-capable peripheral and so treating its > > > presence as a global property isn't right. [...] > > That said, such heuristics should have been a separate patch to make it > > easier to review/drop. > > I think the only right way to get a semi-accurate heuristic is to take > into account the set of dma-capable devices that will use the swiotlb > pool, but that's fiddly and should probably be tackled as a separate > series. Maybe a simpler hack in that direction would be to take the > SWIOTLB_POOL_CC_GUEST if _any_ device is going to use swiotlb? You'll > run into the usual problem of not being able to tell if a device is > DMA-capable or not, but you could probably look for a global restricted > DMA pool and, if that doesn't exist, check for per-device restricted pools > on dma-coherent devices (since restricted DMA isn't supported by ACPI) as > a reasonable approximation. Yes, I think that's reasonable. We'd need to drive this from the arch code or, as you suggested, drivers/virt/coco rather than generic heuristics in the swiotlb code. -- Catalin