From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5D158C433EF for ; Tue, 2 Nov 2021 03:21:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 383A760EE9 for ; Tue, 2 Nov 2021 03:21:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232656AbhKBDXz (ORCPT ); Mon, 1 Nov 2021 23:23:55 -0400 Received: from mailgw01.mediatek.com ([60.244.123.138]:54600 "EHLO mailgw01.mediatek.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S229526AbhKBDXv (ORCPT ); Mon, 1 Nov 2021 23:23:51 -0400 X-UUID: 98af482b8778443ca1aa8da941edd2f1-20211102 X-UUID: 98af482b8778443ca1aa8da941edd2f1-20211102 Received: from mtkcas10.mediatek.inc [(172.21.101.39)] by mailgw01.mediatek.com (envelope-from ) (Generic MTA with TLSv1.2 ECDHE-RSA-AES256-SHA384 256/256) with ESMTP id 571906133; Tue, 02 Nov 2021 11:21:16 +0800 Received: from mtkmbs10n1.mediatek.inc (172.21.101.34) by mtkmbs10n2.mediatek.inc (172.21.101.183) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.792.3; Tue, 2 Nov 2021 11:21:16 +0800 Received: from mtksdccf07 (172.21.84.99) by mtkmbs10n1.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.2.792.15 via Frontend Transport; Tue, 2 Nov 2021 11:21:16 +0800 Message-ID: Subject: Re: [PATCH] dma-direct: fix DMA_ATTR_NO_KERNEL_MAPPING From: Walter Wu To: Ard Biesheuvel CC: Christoph Hellwig , Marek Szyprowski , Robin Murphy , "Matthias Brugger" , Linux IOMMU , Linux Kernel Mailing List , Linux ARM , wsd_upstream , , "Andrew Morton" Date: Tue, 2 Nov 2021 11:21:16 +0800 In-Reply-To: References: <20211101031558.7184-1-walter-zh.wu@mediatek.com> <76840b40fcf26a65467931a73f236982ad39989c.camel@mediatek.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-MTK: N Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2021-11-01 at 15:17 +0100, Ard Biesheuvel wrote: > On Mon, 1 Nov 2021 at 13:21, Walter Wu > wrote: > > > > Hi Ard, > > > > On Mon, 2021-11-01 at 09:34 +0100, Ard Biesheuvel wrote: > > > On Mon, 1 Nov 2021 at 04:17, Walter Wu > > > > > > wrote: > > > > > > > > DMA_ATTR_NO_KERNEL_MAPPING is to avoid creating a kernel > > > > mapping > > > > for the allocated buffer, but current implementation is that > > > > PTE of allocated buffer in kernel page table is valid. So we > > > > should set invalid for PTE of allocate buffer so that there are > > > > no kernel mapping for the allocated buffer. > > > > > > > > In some cases, we don't hope the allocated buffer to be read > > > > by cpu or speculative execution, so we use > > > > DMA_ATTR_NO_KERNEL_MAPPING > > > > to get no kernel mapping in order to achieve this goal. > > > > > > > > Signed-off-by: Walter Wu > > > > Cc: Christoph Hellwig > > > > Cc: Marek Szyprowski > > > > Cc: Robin Murphy > > > > Cc: Matthias Brugger > > > > Cc: Andrew Morton > > > > --- > > > > kernel/dma/direct.c | 8 ++++++++ > > > > 1 file changed, 8 insertions(+) > > > > > > > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c > > > > index 4c6c5e0635e3..aa10b4c5d762 100644 > > > > --- a/kernel/dma/direct.c > > > > +++ b/kernel/dma/direct.c > > > > @@ -13,6 +13,7 @@ > > > > #include > > > > #include > > > > #include > > > > +#include > > > > #include "direct.h" > > > > > > > > /* > > > > @@ -169,6 +170,9 @@ void *dma_direct_alloc(struct device *dev, > > > > size_t size, > > > > if (!PageHighMem(page)) > > > > arch_dma_prep_coherent(page, size); > > > > *dma_handle = phys_to_dma_direct(dev, > > > > page_to_phys(page)); > > > > + /* remove kernel mapping for pages */ > > > > + set_memory_valid((unsigned > > > > long)phys_to_virt(dma_to_phys(dev, *dma_handle)), > > > > + size >> PAGE_SHIFT, 0); > > > > > > This only works if the memory is mapped at page granularity in > > > the > > > linear region, and you cannot rely on that. Many architectures > > > prefer > > > block mappings for the linear region, and arm64 will only use > > > page > > > mappings if rodata=full is set (which is set by default but can > > > be > > > overridden on the kernel command line) > > > > > > > We mainly want to solve arm64 arch. > > Solve what? Our platform is arch64. We need a dynamic allocated buffer from CMA is not to read by CPU peculative execution, so we need to remove its kernel mapping. > > RODATA_FULL_DEFAULT_ENABLED should > > be the arm64 config. If we use CONFIG_RODATA_FULL_DEFAULT_ENABLED > > to > > check whether it call set_memory_valid(). It should avoid other > > architectures. Do you think this method is work? > > > > No. Try it with rodata=off (or rodata=on for that matter) and see > what happens. > I try with rodata=[off/on] on qemu, it looks like boot pass. see below. [ 0.000000] Kernel command line: root=/dev/ram0 rw rootfstype=ext4 rodata=off console=ttyAMA0 rdinit=qemu/ramdisk.img earlyprintk=serial I also try with rodata=off on our platform and do stress test, it looks like pass. Thanks. Walter > > Thanks for your explaination and suggestion. > > > > YW > > > > > > > > > > /* return the page pointer as the opaque cookie > > > > */ > > > > return page; > > > > } > > > > @@ -278,6 +282,10 @@ void dma_direct_free(struct device *dev, > > > > size_t size, > > > > > > > > if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) && > > > > !force_dma_unencrypted(dev) && > > > > !is_swiotlb_for_alloc(dev)) { > > > > + size = PAGE_ALIGN(size); > > > > + /* create kernel mapping for pages */ > > > > + set_memory_valid((unsigned > > > > long)phys_to_virt(dma_to_phys(dev, dma_addr)), > > > > + size >> PAGE_SHIFT, 1); > > > > /* cpu_addr is a struct page cookie, not a > > > > kernel > > > > address */ > > > > dma_free_contiguous(dev, cpu_addr, size); > > > > return; > > > > -- > > > > 2.18.0 > > > > > > > > > > > > _______________________________________________ > > > > linux-arm-kernel mailing list > > > > linux-arm-kernel@lists.infradead.org > > > > > > > > https://urldefense.com/v3/__http://lists.infradead.org/mailman/listinfo/linux-arm-kernel__;!!CTRNKA9wMg0ARbw!16dLCjnvtRkaRLeCO9AQ7Fund5XL0FicZmeVaU3-WkFymr-0lbITfzwrvoJpiHlqnqIu-g$ > > > >