From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay3-d.mail.gandi.net (relay3-d.mail.gandi.net [217.70.183.195]) (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 7DAA4125A4 for ; Tue, 16 Jan 2024 08:23:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ghiti.fr Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ghiti.fr Received: by mail.gandi.net (Postfix) with ESMTPSA id 8398F60002; Tue, 16 Jan 2024 08:23:47 +0000 (UTC) Message-ID: Date: Tue, 16 Jan 2024 09:23:47 +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] riscv: mm: still create swiotlb buffer for kmalloc() bouncing if required Content-Language: en-US To: Jisheng Zhang , Paul Walmsley , Palmer Dabbelt , Albert Ou Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org References: <20231202134224.4029-1-jszhang@kernel.org> From: Alexandre Ghiti In-Reply-To: <20231202134224.4029-1-jszhang@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-GND-Sasl: alex@ghiti.fr Hi Jisheng, On 02/12/2023 14:42, Jisheng Zhang wrote: > After commit f51f7a0fc2f4 ("riscv: enable DMA_BOUNCE_UNALIGNED_KMALLOC > for !dma_coherent"), for non-coherent platforms with less than 4GB > memory, we rely on users to pass "swiotlb=mmnn,force" kernel parameters > to enable DMA bouncing for unaligned kmalloc() buffers. Now let's go > further: If no bouncing needed for ZONE_DMA, let kernel automatically > allocate 1MB swiotlb buffer per 1GB of RAM for kmalloc() bouncing on > non-coherent platforms, so that no need to pass "swiotlb=mmnn,force" > any more. IIUC, DMA_BOUNCE_UNALIGNED_KMALLOC is enabled for all non-coherent platforms, even those with less than 4GB of memory. But the DMA bouncing (which is necessary to enable kmalloc-8/16/32/96...) was not enabled unless the user specified "swiotlb=mmnn,force" on the kernel command line. But does that mean that if the user did not specify "swiotlb=mmnn,force", the kmalloc-8/16/32/96 were enabled anyway and the behaviour was wrong (by lack of DMA bouncing)? I'm trying to understand if that's a fix or an enhancement. Thanks, Alex > > The math of "1MB swiotlb buffer per 1GB of RAM for kmalloc() bouncing" > is taken from arm64. Users can still force smaller swiotlb buffer by > passing "swiotlb=mmnn". > > Signed-off-by: Jisheng Zhang > --- > > since v2: > - fix build error if CONFIG_RISCV_DMA_NONCOHERENT=n > > arch/riscv/include/asm/cache.h | 2 +- > arch/riscv/mm/init.c | 16 +++++++++++++++- > 2 files changed, 16 insertions(+), 2 deletions(-) > > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h > index 2174fe7bac9a..570e9d8acad1 100644 > --- a/arch/riscv/include/asm/cache.h > +++ b/arch/riscv/include/asm/cache.h > @@ -26,8 +26,8 @@ > > #ifndef __ASSEMBLY__ > > -#ifdef CONFIG_RISCV_DMA_NONCOHERENT > extern int dma_cache_alignment; > +#ifdef CONFIG_RISCV_DMA_NONCOHERENT > #define dma_get_cache_alignment dma_get_cache_alignment > static inline int dma_get_cache_alignment(void) > { > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > index 2e011cbddf3a..cbcb9918f721 100644 > --- a/arch/riscv/mm/init.c > +++ b/arch/riscv/mm/init.c > @@ -162,11 +162,25 @@ static void print_vm_layout(void) { } > > void __init mem_init(void) > { > + bool swiotlb = max_pfn > PFN_DOWN(dma32_phys_limit); > #ifdef CONFIG_FLATMEM > BUG_ON(!mem_map); > #endif /* CONFIG_FLATMEM */ > > - swiotlb_init(max_pfn > PFN_DOWN(dma32_phys_limit), SWIOTLB_VERBOSE); > + if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb && > + dma_cache_alignment != 1) { > + /* > + * If no bouncing needed for ZONE_DMA, allocate 1MB swiotlb > + * buffer per 1GB of RAM for kmalloc() bouncing on > + * non-coherent platforms. > + */ > + unsigned long size = > + DIV_ROUND_UP(memblock_phys_mem_size(), 1024); > + swiotlb_adjust_size(min(swiotlb_size_or_default(), size)); > + swiotlb = true; > + } > + > + swiotlb_init(swiotlb, SWIOTLB_VERBOSE); > memblock_free_all(); > > print_vm_layout();