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Sun, 04 Oct 2026 08:09:03 -0700 (PDT) X-Received: by 2002:a05:600c:4453:b0:4a0:2423:946 with SMTP id 5b1f17b1804b1-4a1680f109emr87154015e9.15.1791126543248; Sun, 04 Oct 2026 08:09:03 -0700 (PDT) Received: from px13 ([2a06:5902:822:4600:8c2f:7cc8:bd95:9422]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a027727cecsm272425775e9.9.2026.10.04.08.09.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 04 Oct 2026 08:09:02 -0700 (PDT) Date: Sun, 4 Oct 2026 16:09:00 +0100 From: Chris Bainbridge To: Pratyush Yadav Cc: Mike Rapoport , Pasha Tatashin , Jason Miu , Alexander Graf , Ran Xiaokai , regressions@lists.linux.dev, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org, =?utf-8?B?TWljaGHFgiBDxYJhcGnFhHNraQ==?= Subject: Re: [BUG] KHO handover hangs when memmap reserves PMEM Message-ID: References: <2vxzcxtplh4i.fsf@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2vxzcxtplh4i.fsf@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2C14E40007 X-Stat-Signature: 1389o44p4uxb9ugi74cicm13gzsohmbm X-HE-Tag: 1791126546-612426 X-HE-Meta: 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 I1T6/ZT0 JbqJcdpMxu+Vk3/L+s+4+3iX3U1+spx5mxslZdEbcu3mAOScncxioJG9XuRPU/avrD2Pyi65JsBMAZ3Uc4rAiY2DML22oZqkt8byGdkGCYr33he9kTX7zlE/Cr+CHIdsQauFrXtIhXOe2Q9kRxTElpLgWViMZYJQ7uq2I/GVqCcB4L02vSLMNJKIANoTnRLkgfpF9DjDiM1VGfUiwgKn+hVTkk/yuNK+XJNcphQTo0/2IH1q/U7Wjgzj5T945LcM6ED+er5gSaTso2pZymzxiDC5Ky0HQewqiMj+tvotqIaXlOy8Ub1dOwgtPWXXv3wwthVXrTBTilISvAjkfJi3Yn21Np9SS3/OtVABzHtfiY/5EeE0E+rhkODBVfR8kieHUHsdY7jupHWOlVkg6CuXGUsbOEmHYDxJpmJOCwKfFvDSaXhNy4XpUOpyXXw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Oct 04, 2026 at 03:39:25PM +0200, Pratyush Yadav wrote: > > Just to confirm, the first kernel boots without memmap= right? Yes. > I think the main problem is that the radix tree pages can be anywhere in > memory. So on the first kernel, they can land in an area that the second > kernel's memmap= reserves. So kho_memory_init() might end up using > memory that memmap= reserved. I'm not sure why exactly the next kernel > doesn't produce any output, but IIRC memmap= memory is not mapped to the > direct map, so accessing those pages likely causes a page fault. That's correct, kho_memory_init() page faults. It happens before the serial console is available, so there is no output.