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[34.124.234.44]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c8267735eccsm15998141a12.32.2026.05.13.10.58.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 May 2026 10:58:18 -0700 (PDT) Date: Wed, 13 May 2026 17:58:11 +0000 From: Pranjal Shrivastava To: Jason Gunthorpe Cc: iommu@lists.linux.dev, Joerg Roedel , Robin Murphy , Will Deacon , Alejandro Jimenez , Lu Baolu , Joerg Roedel , Josua Mayer , Kevin Tian , Pasha Tatashin , patches@lists.linux.dev, Samiullah Khawaja , Mostafa Saleh , stable@vger.kernel.org Subject: Re: [PATCH rc 5/5] iommupt: Fix the end_index calculation in __map_range_leaf() Message-ID: References: <0-v1-44b2fef88b25+d3-iommupt_map_rc_jgg@nvidia.com> <5-v1-44b2fef88b25+d3-iommupt_map_rc_jgg@nvidia.com> Precedence: bulk X-Mailing-List: patches@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: <5-v1-44b2fef88b25+d3-iommupt_map_rc_jgg@nvidia.com> On Tue, May 12, 2026 at 01:46:17PM -0300, Jason Gunthorpe wrote: > Sashiko noticed a mismatch of units in this math: num_leaves is > actually the number of leaf *entries* (so a 16-item contiguous leaf > is one num_leaves), while index is in items. The mismatch in maths > causes __map_range_leaf() to exit early instead of efficiently > filling a larger range of contiguous PTEs. > > The early exit is caught by the functions above and then > __map_range_leaf() is re-invoked, so there is no functional issue. > > Correct the misuse of units by adjusting num_leaves with the leaf > size and avoid the performance cost of looping externally. > > There are also some mismatched types for num_leaves; simplify > things to remove the duplicated calculations. > > Fixes: d6c65b0fd621 ("iommupt: Avoid rewalking during map") > Signed-off-by: Jason Gunthorpe This is an important catch! It means that today, we were redundantly re-walking the upper page table levels. Reviewd-by: Pranjal Shrivastava Thanks!