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 A56D84CDDD6; Thu, 17 Sep 2026 16:02:56 +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=1789660978; cv=none; b=D6eQxmnn4hasuwLV4f1+grpmV52XLaqGr/rButdoazEWP3PG8Sgq041bECIc8WUhw2m+qvX4BnV6PlEpLgXDDF1UyZnBKAyeB8SF77oIrDQqiBzuMbf+Y4iiBo15LRUQNZaLPn7wBADj2sOFHnNS0KI9nCs/rMi6cJOrqHb6ff8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789660978; c=relaxed/simple; bh=oTSpkmkdrCN17NbG/BBwkxPXVynnbNeoywXS03zePeY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ane3u51g49s7i0UOvRxL1WRJKkrnzaPY2Dsw/iURS+lMgSLrB5BdeJRicBnzQ4Ce0MrbeVCUpEOlP/ZRkW9pbZMRRJtjGrc2nqXdsJHIggs55gDDrzM++gWyJajQE/69O7G6lpTti7256Pt5qTmY/pE34GxPVjortnKyLvEo/E4= 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=S2fxmt5n; 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="S2fxmt5n" 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 676491476; Thu, 17 Sep 2026 09:02:52 -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 0676E3F7B4; Thu, 17 Sep 2026 09:02:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1789660976; bh=oTSpkmkdrCN17NbG/BBwkxPXVynnbNeoywXS03zePeY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=S2fxmt5n7wqW8D4QzBKWm8vc57hZzAXsLdw9Jtmn7fDwYuUkUjAjjz0iYC6XiR0tu 9uTMew8t9VAK7rJOxWX62e/iXJau/fZJ5mkD/AXyBAM4cL0DOiEE+aa31dFygWVPu6 NIHL5WfGiIh7klKkEub7eNcTGfyNDO5DXPYwmJRI= Date: Thu, 17 Sep 2026 17:02:48 +0100 From: Catalin Marinas To: "Aneesh Kumar K.V (Arm)" Cc: iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Robin Murphy , Marek Szyprowski , Will Deacon , 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)" , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Russell King , Huacai Chen , Thomas Bogendoerfer , Jiaxun Yang , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , 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 v4 3/5] dma: swiotlb: Centralize memory-encryption pool sizing Message-ID: References: <20260914070135.313337-1-aneesh.kumar@kernel.org> <20260914070135.313337-4-aneesh.kumar@kernel.org> Precedence: bulk X-Mailing-List: loongarch@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260914070135.313337-4-aneesh.kumar@kernel.org> On Mon, Sep 14, 2026 at 12:31:32PM +0530, Aneesh Kumar K.V (Arm) wrote: > +/** > + * swiotlb_adjusted_size() - get the prospective adjusted SWIOTLB size > + * > + * Return the size that confidential-computing guest sizing would select for > + * the default pool, without changing the configured SWIOTLB size. An > + * explicit swiotlb= size is always preserved. An explicit area count is > + * included in the size calculation. Automatic area sizing is initialized > + * later from the running kernel's possible CPU map and any resulting size > + * adjustment is therefore not reflected in the returned size. > + */ > +unsigned long __init swiotlb_adjusted_size(void) > +{ > + unsigned long nslabs, size = swiotlb_size_or_default(); > + > + if (swiotlb_default_size_changed() || > + !cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) > + return size; > + /* > + * For SEV and TDX and CCA, all DMA has to occur via > + * shared/unencrypted pages. Kernel uses SWIOTLB to make this > + * happen without changing device drivers. However, depending on > + * the workload being run, the default 64MB of SWIOTLB may not be > + * enough and SWIOTLB may run out of buffers for DMA, resulting in > + * I/O errors and/or performance degradation especially with high > + * I/O workloads. > + * > + * Adjust the default size of SWIOTLB using a percentage of guest > + * memory for SWIOTLB buffers. Also, as the SWIOTLB bounce buffer > + * memory is allocated from low memory, ensure that the adjusted > + * size is within the limits of low available memory. Nit: if SWIOTLB_ANY is passed, do we still allocate only from low memory? I think this comment made sense on x86 but it's not valid for s390, pseries with the changes so far. Otherwise: Reviewed-by: Catalin Marinas