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[34.140.140.54]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-477bf1e86b3sm239817465e9.6.2025.11.24.08.02.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Nov 2025 08:02:01 -0800 (PST) Date: Mon, 24 Nov 2025 16:01:58 +0000 From: Mostafa Saleh To: Will Deacon 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 3/4] drivers/iommu-debug-pagealloc: Track IOMMU pages Message-ID: References: <20251106163953.1971067-1-smostafa@google.com> <20251106163953.1971067-4-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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Nov 24, 2025 at 03:35:47PM +0000, Will Deacon wrote: > On Mon, Nov 24, 2025 at 12:37:31PM +0000, Mostafa Saleh wrote: > > On Thu, Nov 13, 2025 at 11:00:29AM +0000, Will Deacon wrote: > > > On Thu, Nov 06, 2025 at 04:39:52PM +0000, Mostafa Saleh wrote: > > > > Using the new calls, use an atomic refcount to track how many times > > > > a page is mapped in any of the IOMMUs. > > > > > > > > For unmap we need to use iova_to_phys() to get the physical address > > > > of the pages. > > > > > > > > We use the smallest supported page size as the granularity of tracking > > > > per domain. > > > > This is important as it possible to map pages and unmap them with > > > > larger sizes (as in map_sg()) cases. > > > > > > > > Signed-off-by: Mostafa Saleh > > > > Tested-by: Qinxin Xia > > > > --- > > > > drivers/iommu/iommu-debug-pagealloc.c | 74 +++++++++++++++++++++++++++ > > > > 1 file changed, 74 insertions(+) > > > > > > > > diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c > > > > index a6a2f844b09d..0e14104b971c 100644 > > > > --- a/drivers/iommu/iommu-debug-pagealloc.c > > > > +++ b/drivers/iommu/iommu-debug-pagealloc.c > > > > @@ -27,16 +27,90 @@ struct page_ext_operations page_iommu_debug_ops = { > > > > .need = need_iommu_debug, > > > > }; > > > > > > > > +static struct page_ext *get_iommu_page_ext(phys_addr_t phys) > > > > +{ > > > > + struct page *page = phys_to_page(phys); > > > > + struct page_ext *page_ext = page_ext_get(page); > > > > + > > > > + return page_ext; > > > > +} > > > > + > > > > +static struct iommu_debug_metadate *get_iommu_data(struct page_ext *page_ext) > > > > +{ > > > > + return page_ext_data(page_ext, &page_iommu_debug_ops); > > > > +} > > > > + > > > > +static void iommu_debug_inc_page(phys_addr_t phys) > > > > +{ > > > > + struct page_ext *page_ext = get_iommu_page_ext(phys); > > > > + struct iommu_debug_metadate *d = get_iommu_data(page_ext); > > > > + > > > > + WARN_ON(atomic_inc_return(&d->ref) <= 0); > > > > > > Is it worth dumping some information about the page in addition to the > > > WARN_ON()? That way, you might be able to benefit from other debug > > > options (e.g. PAGE_OWNER) if they are enabled. > > > > These WARN_ON are for overflows, which should never happen. > > I initially thought about using the refcount_t, but it didn’t seem > > suitable as refcount_add() expects that the refcount is already “1” > > indicating that an object was already created which doesn’t fit > > in the semantics of what this is. Similar for refcount_dec(). > > > > In the next patch there is a WARN_ON for the refcount check > > to capture the mis-behaving context, I will add a debug print with > > the leaked physical address in that case as this is the important one. > > I was thinking specifically about calling dump_page_owner(). I see, that makes sense. Thanks, Mostafa > > Will