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X-CSE-ConnectionGUID: N0kVG/r0Q1Kms0EgPFrPzA== X-CSE-MsgGUID: lBo3AaDYREiFrQVRQ6E6kA== X-IronPort-AV: E=McAfee;i="6800,10657,11642"; a="70247995" X-IronPort-AV: E=Sophos;i="6.21,150,1763452800"; d="scan'208";a="70247995" Received: from orviesa003.jf.intel.com ([10.64.159.143]) by fmvoesa107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Dec 2025 19:35:31 -0800 X-CSE-ConnectionGUID: Ov4Ez70WS2iVEsI0s1KPLg== X-CSE-MsgGUID: xGKqUxKKQH+p43hn9drWLA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,150,1763452800"; d="scan'208";a="201797741" Received: from allen-sbox.sh.intel.com (HELO [10.239.159.30]) ([10.239.159.30]) by ORVIESA003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Dec 2025 19:35:27 -0800 Message-ID: <7186caa3-13c0-4629-a07f-162c00138ad9@linux.intel.com> Date: Mon, 15 Dec 2025 11:30:39 +0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/4] iommu: Add calls for IOMMU_DEBUG_PAGEALLOC 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, will@kernel.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, xiaqinxin@huawei.com, rdunlap@infradead.org References: <20251211125928.3258905-1-smostafa@google.com> <20251211125928.3258905-3-smostafa@google.com> <20e015d7-cb54-4a2a-bf62-a828e10e3126@linux.intel.com> Content-Language: en-US From: Baolu Lu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 12/13/25 02:44, Mostafa Saleh wrote: > On Fri, Dec 12, 2025 at 10:33:20AM +0800, Baolu Lu wrote: >> On 12/11/25 20:59, Mostafa Saleh wrote: >>> Add calls for the new iommu debug config IOMMU_DEBUG_PAGEALLOC: >>> - iommu_debug_init: Enable the debug mode if configured by the user. >>> - iommu_debug_map: Track iommu pages mapped, using physical address. >>> - iommu_debug_unmap_begin: Track start of iommu unmap operation, with >>> IOVA and size. >>> - iommu_debug_unmap_end: Track the end of unmap operation, passing the >>> actual unmapped size versus the tracked one at unmap_begin. >>> >>> We have to do the unmap_begin/end as once pages are unmapped we lose >>> the information of the physical address. >>> This is racy, but the API is racy by construction as it uses refcounts >>> and doesn't attempt to lock/synchronize with the IOMMU API as that will >>> be costly, meaning that possibility of false negative exists. >>> >>> Signed-off-by: Mostafa Saleh >>> --- >>> drivers/iommu/iommu-debug-pagealloc.c | 28 +++++++++++++ >>> drivers/iommu/iommu-priv.h | 58 +++++++++++++++++++++++++++ >>> drivers/iommu/iommu.c | 11 ++++- >>> include/linux/iommu-debug-pagealloc.h | 1 + >>> 4 files changed, 96 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c >>> index 4022e9af7f27..1d343421da98 100644 >>> --- a/drivers/iommu/iommu-debug-pagealloc.c >>> +++ b/drivers/iommu/iommu-debug-pagealloc.c >>> @@ -5,11 +5,15 @@ >>> * IOMMU API debug page alloc sanitizer >>> */ >>> #include >>> +#include >>> #include >>> #include >>> #include >>> +#include "iommu-priv.h" >>> + >>> static bool needed; >>> +DEFINE_STATIC_KEY_FALSE(iommu_debug_initialized); >>> struct iommu_debug_metadata { >>> atomic_t ref; >>> @@ -25,6 +29,30 @@ struct page_ext_operations page_iommu_debug_ops = { >>> .need = need_iommu_debug, >>> }; >>> +void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, size_t size) >>> +{ >>> +} >>> + >>> +void __iommu_debug_unmap_begin(struct iommu_domain *domain, >>> + unsigned long iova, size_t size) >>> +{ >>> +} >>> + >>> +void __iommu_debug_unmap_end(struct iommu_domain *domain, >>> + unsigned long iova, size_t size, >>> + size_t unmapped) >>> +{ >>> +} >>> + >>> +void iommu_debug_init(void) >>> +{ >>> + if (!needed) >>> + return; >>> + >>> + pr_info("iommu: Debugging page allocations, expect overhead or disable iommu.debug_pagealloc"); >>> + static_branch_enable(&iommu_debug_initialized); >>> +} >>> + >>> static int __init iommu_debug_pagealloc(char *str) >>> { >>> return kstrtobool(str, &needed); >>> diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h >>> index c95394cd03a7..aaffad5854fc 100644 >>> --- a/drivers/iommu/iommu-priv.h >>> +++ b/drivers/iommu/iommu-priv.h >>> @@ -5,6 +5,7 @@ >>> #define __LINUX_IOMMU_PRIV_H >>> #include >>> +#include >>> #include >>> static inline const struct iommu_ops *dev_iommu_ops(struct device *dev) >>> @@ -65,4 +66,61 @@ static inline int iommufd_sw_msi(struct iommu_domain *domain, >>> int iommu_replace_device_pasid(struct iommu_domain *domain, >>> struct device *dev, ioasid_t pasid, >>> struct iommu_attach_handle *handle); >>> + >>> +#ifdef CONFIG_IOMMU_DEBUG_PAGEALLOC >>> + >>> +void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, >>> + size_t size); >>> +void __iommu_debug_unmap_begin(struct iommu_domain *domain, >>> + unsigned long iova, size_t size); >>> +void __iommu_debug_unmap_end(struct iommu_domain *domain, >>> + unsigned long iova, size_t size, size_t unmapped); >>> + >>> +static inline void iommu_debug_map(struct iommu_domain *domain, >>> + phys_addr_t phys, size_t size) >>> +{ >>> + if (static_branch_unlikely(&iommu_debug_initialized)) >>> + __iommu_debug_map(domain, phys, size); >>> +} >>> + >>> +static inline void iommu_debug_unmap_begin(struct iommu_domain *domain, >>> + unsigned long iova, size_t size) >>> +{ >>> + if (static_branch_unlikely(&iommu_debug_initialized)) >>> + __iommu_debug_unmap_begin(domain, iova, size); >>> +} >>> + >>> +static inline void iommu_debug_unmap_end(struct iommu_domain *domain, >>> + unsigned long iova, size_t size, >>> + size_t unmapped) >>> +{ >>> + if (static_branch_unlikely(&iommu_debug_initialized)) >>> + __iommu_debug_unmap_end(domain, iova, size, unmapped); >>> +} >> I am wondering whether it would be better if we move iommu_debug_map() >> to iommu-debug-pagealloc.c, >> >> void iommu_debug_map(struct iommu_domain *domain, >> phys_addr_t phys, size_t size) >> { >> if (static_branch_likely(&iommu_debug_initialized)) >> __iommu_debug_map(domain, phys, size); >> } >> >> (Does it make sense to use static_branch_likely() here? Normally, people >> who enable CONFIG_IOMMU_DEBUG_PAGEALLOC would want to use this >> debugging feature. Or not?) >> >> So that ... > This actually was the v1 implementation [1], but Jörg suggested to move > it to a header file as a function call would have an overhead if this > feautre is disabled. > > I believe the priority would be to keep the performance overhead minimal > with CONFIG_IOMMU_DEBUG_PAGEALLOC and the commandline disabled, so people > can run with the config in production and only enable the commandline > it to debug problems, without having overhead on the typical case. Okay, fair enough. Thanks, baolu