From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 E781A946C; Thu, 13 Nov 2025 10:05:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763028327; cv=none; b=XBeJwWt1dPhVtVVowNczw28EmAlj6Gg4gEjfMKVOzj2k5Lr3gp2K2HTYhr7UtUMteP9wKbIEZw8nbfCEWTpGDYkGHtAlQ4CaUW1WE9oiC4lt2YpfIqE+BkUAAFoo2JvXDJ89iA0GXNrJDCbLSqbDZJCdMYab8VfwnsspoTseHb0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763028327; c=relaxed/simple; bh=BLTb5heskjXzTldos1Pbf98tCoJwck1drSSFzaVhr3s=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gs9bmk9wqqSxegSQbDo/mDq2vOhxhSQqHnqUPtP271OFRJ61w41R/SXjSQVGfbneDsE38b0yeskUg8ynNu74FAcW7TGkse9znTN5Pwv8JmubRQMExR66a31yfLkxloJpqFpILGxgjLw9PU2MSS5YC74H+pcDfcIMsvlLxqN/vIw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KB4GxgXq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="KB4GxgXq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C075AC4CEF1; Thu, 13 Nov 2025 10:05:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763028326; bh=BLTb5heskjXzTldos1Pbf98tCoJwck1drSSFzaVhr3s=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KB4GxgXqJZ7cO7XBy6/guf626zim6beEsg/YfQpCnDOK4CIsFLP+coyBB5LQx6Ybb I7s2JOUvrf+DC7c4xVdeR/uJQIhZpbiDJGmjcLEhP+OEhRO1+tbsNZG6fuOByhSJgv hrWjyJWa5kG9pfQAPvUoU/pHuUUk5rTrKamkIEBUA+G0CgjhCtK37Erfyu+rqbuvOS 1dlhMdtne37nyvq7Z/8tU5sJt3/Nqm6oEBR+LDczDAuItX4mBgczhd8bAdZ7MliWdx jGvHbgZSquL92vYPhyoBVwk+3NUER/r21+FimVga8kmJjEWv6mD2TE90Sd0NpsNNX1 bpUdQLOkX6ukA== Date: Thu, 13 Nov 2025 10:05:19 +0000 From: Will Deacon To: Mostafa Saleh Cc: linux-mm@kvack.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, corbet@lwn.net, joro@8bytes.org, robin.murphy@arm.com, akpm@linux-foundation.org, vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, rppt@kernel.org, Qinxin Xia Subject: Re: [PATCH v2 1/4] drivers/iommu: Add page_ext for IOMMU_DEBUG_PAGEALLOC Message-ID: References: <20251106163953.1971067-1-smostafa@google.com> <20251106163953.1971067-2-smostafa@google.com> Precedence: bulk X-Mailing-List: linux-doc@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: <20251106163953.1971067-2-smostafa@google.com> Hi Mostafa, On Thu, Nov 06, 2025 at 04:39:50PM +0000, Mostafa Saleh wrote: > Add a new config IOMMU_DEBUG_PAGEALLOC, which registers new data to > page_ext. > This config will be used by the IOMMU API to track pages mapped in > the IOMMU to catch drivers trying to free kernel memory that they > still map in their domains, causing all types of memory corruption. > This behaviour is disabled by default and can be enabled using > kernel cmdline iommu.debug_pagealloc. > > Signed-off-by: Mostafa Saleh > Tested-by: Qinxin Xia > --- > .../admin-guide/kernel-parameters.txt | 6 ++++ > drivers/iommu/Kconfig | 15 +++++++++ > drivers/iommu/Makefile | 1 + > drivers/iommu/iommu-debug-pagealloc.c | 32 +++++++++++++++++++ > include/linux/iommu-debug-pagealloc.h | 17 ++++++++++ > mm/page_ext.c | 4 +++ > 6 files changed, 75 insertions(+) > create mode 100644 drivers/iommu/iommu-debug-pagealloc.c > create mode 100644 include/linux/iommu-debug-pagealloc.h This looks like a pretty handy feature to me, but I have some nits below. > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 6c42061ca20e..9a1c4ac8ba96 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -2557,6 +2557,12 @@ > 1 - Bypass the IOMMU for DMA. > unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. > > + iommu.debug_pagealloc= > + [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this > + parameter enables the feature at boot time. By default, it > + is disabled and the system will work mostly the same as a > + kernel built without CONFIG_IOMMU_DEBUG_PAGEALLOC. Can you be more specific about "mostly the same"? > + > io7= [HW] IO7 for Marvel-based Alpha systems > See comment before marvel_specify_io7 in > arch/alpha/kernel/core_marvel.c. > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig > index 70d29b14d851..6b5e9a2d936a 100644 > --- a/drivers/iommu/Kconfig > +++ b/drivers/iommu/Kconfig > @@ -383,4 +383,19 @@ config SPRD_IOMMU > > Say Y here if you want to use the multimedia devices listed above. > > +config IOMMU_DEBUG_PAGEALLOC > + bool "Debug page memory allocations against IOMMU" Perhaps "IOMMU mappings" would make this a little clearer? > + depends on DEBUG_PAGEALLOC && IOMMU_API && PAGE_EXTENSION > + help > + This config checks that a page is freed(unmapped) or mapped by the > + kernel is not mapped in any IOMMU domain. I can't really parse this sentence :/ > It can help with debugging > + use-after-free or out-of-bound maps from drivers doing DMA through > + the IOMMU API. > + This santaizer can have false-negative cases where some problems > + won't be detected. Maybe just say "The sanitizer is best-effort and can fail to detect problems in the case that ...". > + Expect overhead when enabling this and enabling the kernel command > + line iommu.debug_pagealloc. I'd reword this to say something like "Due to the overhead of the sanitiser, iommu.debug_pagealloc must also be passed on the kernel command-line to enable this feature". > + > + If unsure, say N here. > + > endif # IOMMU_SUPPORT > diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile > index 355294fa9033..8f5130b6a671 100644 > --- a/drivers/iommu/Makefile > +++ b/drivers/iommu/Makefile > @@ -34,3 +34,4 @@ obj-$(CONFIG_IOMMU_SVA) += iommu-sva.o > obj-$(CONFIG_IOMMU_IOPF) += io-pgfault.o > obj-$(CONFIG_SPRD_IOMMU) += sprd-iommu.o > obj-$(CONFIG_APPLE_DART) += apple-dart.o > +obj-$(CONFIG_IOMMU_DEBUG_PAGEALLOC) += iommu-debug-pagealloc.o > diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c > new file mode 100644 > index 000000000000..385c8bfae02b > --- /dev/null > +++ b/drivers/iommu/iommu-debug-pagealloc.c > @@ -0,0 +1,32 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * Copyright (C) 2025 - Google Inc > + * Author: Mostafa Saleh > + * IOMMU API debug page alloc sanitizer > + */ > +#include > +#include > +#include > +#include > + > +static bool needed; > + > +struct iommu_debug_metadate { > + atomic_t ref; > +}; s/metadate/metadata/ Will