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[35.187.245.222]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a3e3c3a2ecsm110215965ad.6.2026.01.09.11.15.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Jan 2026 11:15:25 -0800 (PST) Date: Fri, 9 Jan 2026 19:15:18 +0000 From: Pranjal Shrivastava 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, baolu.lu@linux.intel.com, rdunlap@infradead.org, Samiullah Khawaja Subject: Re: [PATCH v6 3/4] iommu: debug-pagealloc: Track IOMMU pages Message-ID: References: <20260109171805.901995-1-smostafa@google.com> <20260109171805.901995-4-smostafa@google.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260109171805.901995-4-smostafa@google.com> On Fri, Jan 09, 2026 at 05:18:04PM +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 is possible to map pages and unmap them with > larger sizes (as in map_sg()) cases. > > Reviewed-by: Samiullah Khawaja > Reviewed-by: Lu Baolu > Signed-off-by: Mostafa Saleh > --- > drivers/iommu/iommu-debug-pagealloc.c | 84 +++++++++++++++++++++++++++ > 1 file changed, 84 insertions(+) > > diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c > index 1d343421da98..9eb49e1230ee 100644 > --- a/drivers/iommu/iommu-debug-pagealloc.c > +++ b/drivers/iommu/iommu-debug-pagealloc.c > @@ -29,19 +29,103 @@ 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_metadata *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_metadata *d = get_iommu_data(page_ext); > + > + WARN_ON(atomic_inc_return_relaxed(&d->ref) <= 0); > + page_ext_put(page_ext); > +} > + > +static void iommu_debug_dec_page(phys_addr_t phys) > +{ > + struct page_ext *page_ext = get_iommu_page_ext(phys); > + struct iommu_debug_metadata *d = get_iommu_data(page_ext); > + > + WARN_ON(atomic_dec_return_relaxed(&d->ref) < 0); > + page_ext_put(page_ext); > +} > + > +/* > + * IOMMU page size doesn't have to match the CPU page size. So, we use > + * the smallest IOMMU page size to refcount the pages in the vmemmap. > + * That is important as both map and unmap has to use the same page size > + * to update the refcount to avoid double counting the same page. > + * And as we can't know from iommu_unmap() what was the original page size > + * used for map, we just use the minimum supported one for both. > + */ > +static size_t iommu_debug_page_size(struct iommu_domain *domain) > +{ > + return 1UL << __ffs(domain->pgsize_bitmap); > +} > + > void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, size_t size) > { > + size_t off, end; > + size_t page_size = iommu_debug_page_size(domain); > + > + if (WARN_ON(!phys || check_add_overflow(phys, size, &end))) > + return; > + > + for (off = 0 ; off < size ; off += page_size) { > + if (!pfn_valid(__phys_to_pfn(phys + off))) > + continue; > + iommu_debug_inc_page(phys + off); > + } > +} > + > +static void __iommu_debug_update_iova(struct iommu_domain *domain, > + unsigned long iova, size_t size, bool inc) > +{ > + size_t off, end; > + size_t page_size = iommu_debug_page_size(domain); > + > + if (WARN_ON(check_add_overflow(iova, size, &end))) > + return; > + > + for (off = 0 ; off < size ; off += page_size) { > + phys_addr_t phys = iommu_iova_to_phys(domain, iova + off); > + > + if (!phys || !pfn_valid(__phys_to_pfn(phys))) > + continue; > + > + if (inc) > + iommu_debug_inc_page(phys); > + else > + iommu_debug_dec_page(phys); > + } > } > > void __iommu_debug_unmap_begin(struct iommu_domain *domain, > unsigned long iova, size_t size) > { > + __iommu_debug_update_iova(domain, iova, size, false); > } > > void __iommu_debug_unmap_end(struct iommu_domain *domain, > unsigned long iova, size_t size, > size_t unmapped) > { > + if ((unmapped == size) || WARN_ON_ONCE(unmapped > size)) > + return; > + Looks good! > + /* If unmap failed, re-increment the refcount. */ > + __iommu_debug_update_iova(domain, iova + unmapped, > + size - unmapped, true); > } > Reviewed-by: Pranjal Shrivastava Thanks! > void iommu_debug_init(void) > -- > 2.52.0.457.g6b5491de43-goog > >