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dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from LY0PR12MB727857.namprd12.prod.outlook.com (2603:10b6:408:3ba::5) by MN2PR12MB4358.namprd12.prod.outlook.com (2603:10b6:208:24f::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.592.10; Thu, 5 Nov 2026 16:28:36 +0000 Received: from LY0PR12MB727857.namprd12.prod.outlook.com ([fe80::843e:82cd:41ca:f522]) by LY0PR12MB727857.namprd12.prod.outlook.com ([fe80::843e:82cd:41ca:f522%5]) with mapi id 15.21.0592.009; Thu, 5 Nov 2026 16:28:36 +0000 Message-ID: Date: Thu, 5 Nov 2026 08:28:32 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v16 13/18] cxl: Validate and synchronize HDM ranges around reset To: Richard Cheng Cc: Alison Schofield , Bjorn Helgaas , Dave Jiang , Davidlohr Bueso , Ira Weiny , Jonathan Cameron , Vishal Verma , linux-cxl@vger.kernel.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Li Ming , Alex Williamson , vsethi@nvidia.com, alwilliamson@nvidia.com, Sai Yashwanth Reddy Kancherla , Vishal Aslot , Manish Honap , Jiandi An , linux-tegra@vger.kernel.org References: <20261029145703.2185231-1-smadhavan@nvidia.com> <20261029145703.2185231-14-smadhavan@nvidia.com> Content-Language: en-US From: Srirangan Madhavan In-Reply-To: Content-Type: text/plain; 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>> + >> + lockdep_assert_held_write(&cxl_rwsem.region); >> + >> + list_for_each_entry(range, &q->ranges, list) { >> + const struct range *hpa_range = &range->hpa_range; >> + >> + range->res = request_mem_region(hpa_range->start, range->len, >> + "cxl_reset"); >> + if (!range->res) >> + return -EBUSY; >> + } >> + > Hi Srirangan, > > The spec explicitly requires no outstanding or new CXL.mem transaction after > the affected HDM ranges are offlined. > > For this part, I don't see any guarantee that a successful request_mem_region() > means all outstanding memory access have stopped and no new access can occur. > > I see you refuse to reset when resource reservation conflict, but nothing > offline memory or directly stop CXL.mem traffic. > > I wonder if the implementation provide enough evidence that when request_mem_region() > success means no new mem access or CXL.mem traffic will pop up ? > > Best regards, > Richard Cheng. Hi Richard, You are right that a successful request_mem_region() does not show that no CXL.mem traffic can occur. The design expects userspace to offline CXL.mem users before reset, as discussed earlier. The reservation enforces that for claimed ranges: the reset fails while a conflicting resource is claimed, and nobody can claim the range during the reset. It cannot see code that uses the range without claiming it. That case is also covered by the offline expectation, not by the reservation. I added this to the patch 13 commit message in v17 instead of leaving it implicit. -- Regards, Srirangan