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[159.2.73.22]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8d5e69afdb6sm667396385a.40.2026.04.06.18.27.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Apr 2026 18:27:27 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1w9vDy-0000000EAWd-481U; Mon, 06 Apr 2026 22:27:26 -0300 Date: Mon, 6 Apr 2026 22:27:26 -0300 From: Jason Gunthorpe To: Sina Hassani Cc: kevin.tian@intel.com, joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Aaron Wisner , stable@vger.kernel.org Subject: Re: [PATCH v2] Fixes a race in iopt_unmap_iova_range Message-ID: <20260407012726.GN2551565@ziepe.ca> References: <20260407011210.GM2551565@ziepe.ca> Precedence: bulk X-Mailing-List: linux-kernel@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, Apr 06, 2026 at 06:17:24PM -0700, Sina Hassani wrote: > On Mon, Apr 6, 2026 at 6:12 PM Jason Gunthorpe wrote: > > > > On Mon, Apr 06, 2026 at 04:07:01PM -0700, Sina Hassani wrote: > > > > > io_pagetable *iopt, unsigned long start, > > > unmapped_bytes += area_last - area_first + 1; > > > > > > down_write(&iopt->iova_rwsem); > > > + > > > + /* Do not reconsider things already unmapped in case of > > > + * concurrent allocation */ > > > + start = area_last + 1; > > > > area_last can be ULONG_MAX so this literally overflows to 0. It is why > > I formed the suggestion I gave as I did > > > Yes, in which case the if (start < area_last) that follows will catch > it. Are you suggesting I compare against ULONG_MAX instead? iommufd does not have any overflows to 0 and rely on it tricks like this. You should just compare to the existing iteration last Jason