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[142.167.219.86]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6f4c0aae668sm8460536d6.113.2025.04.24.05.07.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Apr 2025 05:07:03 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1u7vM7-00000007TSP-0PWP; Thu, 24 Apr 2025 09:07:03 -0300 Date: Thu, 24 Apr 2025 09:07:03 -0300 From: Jason Gunthorpe To: Leon Romanovsky Cc: Christoph Hellwig , Mika =?utf-8?B?UGVudHRpbMOk?= , Marek Szyprowski , Jens Axboe , Keith Busch , Jake Edge , Jonathan Corbet , Zhu Yanjun , Robin Murphy , Joerg Roedel , Will Deacon , Sagi Grimberg , Bjorn Helgaas , Logan Gunthorpe , Yishai Hadas , Shameer Kolothum , Kevin Tian , Alex Williamson , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Andrew Morton , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, Niklas Schnelle , Chuck Lever , Luis Chamberlain , Matthew Wilcox , Dan Williams , Kanchan Joshi , Chaitanya Kulkarni Subject: Re: [PATCH v9 10/24] mm/hmm: let users to tag specific PFN with DMA mapped bit Message-ID: <20250424120703.GY1213339@ziepe.ca> References: <0a7c1e06269eee12ff8912fe0da4b7692081fcde.1745394536.git.leon@kernel.org> <7185c055-fc9e-4510-a9bf-6245673f2f92@redhat.com> <20250423181706.GT1213339@ziepe.ca> <36891b0e-d5fa-4cf8-a181-599a20af1da3@redhat.com> <20250423233335.GW1213339@ziepe.ca> <20250424080744.GP48485@unreal> <20250424081101.GA22989@lst.de> <20250424084626.GQ48485@unreal> 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=us-ascii Content-Disposition: inline In-Reply-To: <20250424084626.GQ48485@unreal> On Thu, Apr 24, 2025 at 11:46:26AM +0300, Leon Romanovsky wrote: > On Thu, Apr 24, 2025 at 10:11:01AM +0200, Christoph Hellwig wrote: > > On Thu, Apr 24, 2025 at 11:07:44AM +0300, Leon Romanovsky wrote: > > > > I see, so yes order occupies 5 bits [-4,-5,-6,-7,-8] and the > > > > DMA_MAPPED overlaps, it should be 9 not 7 because of the backwardness. > > > > > > Thanks for the fix. > > > > Maybe we can use the chance to make the scheme less fragile? i.e. > > put flags in the high bits and derive the first valid bit from the > > pfn order? > > It can be done too. This is what I got: Use genmask: enum hmm_pfn_flags { HMM_FLAGS_START = BITS_PER_LONG - PAGE_SHIFT, HMM_PFN_FLAGS = GENMASK(BITS_PER_LONG - 1, HMM_FLAGS_START), /* Output fields and flags */ HMM_PFN_VALID = 1UL << HMM_FLAGS_START + 0, HMM_PFN_WRITE = 1UL << HMM_FLAGS_START + 1, HMM_PFN_ERROR = 1UL << HMM_FLAGS_START + 2, HMM_PFN_ORDER_MASK = GENMASK(HMM_FLAGS_START + 7, HMM_FLAGS_START + 3), /* Input flags */ HMM_PFN_REQ_FAULT = HMM_PFN_VALID, HMM_PFN_REQ_WRITE = HMM_PFN_WRITE, }; Jason