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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-88652b90ebasm91346316d6.55.2025.12.01.15.01.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Dec 2025 15:01:46 -0800 (PST) Date: Mon, 1 Dec 2025 18:01:45 -0500 From: Gregory Price To: balbirs@nvidia.com Cc: linux-kernel@vger.kernel.org, dan.j.williams@intel.com, x86@kernel.org, Christian =?iso-8859-1?Q?K=F6nig?= , Ingo Molnar , Kees Cook , Bjorn Helgaas , Linus Torvalds , Peter Zijlstra , Andy Lutomirski , Alex Deucher , Bert Karwatzki , Madhavan Srinivasan , Nicholas Piggin , linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] arch/x86: memory_hotplug, do not bump up max_pfn for device private pages Message-ID: References: <20250401000752.249348-1-balbirs@nvidia.com> <692e1297e3b6_261c110064@dwillia2-mobl4.notmuch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <692e1297e3b6_261c110064@dwillia2-mobl4.notmuch> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4D782A001E X-Stat-Signature: 8e9hhw4ocjn9foi5aobdu66i5f3t7x6z X-Rspam-User: X-HE-Tag: 1764630113-892592 X-HE-Meta: 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 uL5+Vk1c Z8UU5NsHMt721Nn5gb1IYOkFtulaqSctWbS3mcKj0Xf8XoPVSnYfO8llL80L7u6sZzu9X/jCSj1jpS5lLX3o2TogaTK+YzvUkE14qu3cOfHDiYplvRCziSKsMTlSPKYV61uir3E8C6vEtpJy/00I7hJ4p/BJknlKLpy5DbMsGcwa36X2cyDrhncKq0v5mDsfKVrL1p26rPw80ryeMHgOce+bMHSxANRs+O7oYyHr2b12zUDcJ5PWgocXWvv30oTBW5VuWmcplU/aXkENceNJVKjFCfyX2IjQuKIZtRwrsJsbeYSROqlIYHw+e8nZtyRBwYVN/bxvg0lPMRaYyaFo9Fu8zWgl1rNB5PuVoaFztVNc2GgljocHaBY45UoGDLDwomkYz5H9kew1Hpu3CckIRL7gv/Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Dec 01, 2025 at 02:11:35PM -0800, dan.j.williams@intel.com wrote: > [ add Gregory and linux-mm ] > > [ full context for new Cc: ] > Balbir Singh wrote: > > Commit 7ffb791423c7 ("x86/kaslr: Reduce KASLR entropy on most x86 systems") > > exposed a bug with nokaslr and zone device > > interaction, as seen on a system with an AMD iGPU and dGPU (see [1]). > > The root cause of the issue is that, the gpu driver registers a zone ^^^^^^^^^^^^^^ which one, iGPU or dGPU? or they managed by the same driver? (sorry, stickler for vagueness) > > Fix this by not bumping up max_pfn on x86 systems, when pgmap is passed > > into add_pages(). The presence of pgmap is used to determine if device > > private memory is being added via add_pages(). > > Concur with Dan's take below here, please check for DEVICE_PRIVATE so as not to affect DEVICE_COHERENT. Or if there's a reason to affect DEVICE_COHERENT, please explain here. > > arch/powerpc is also impacted by this bug, this patch does not fix > > the issue for powerpc. > > > > I've left powerpc out of this regression change due to the time required > > to setup and test via qemu. I wanted to address the regression quickly > > At least +Cc ppc folks to take a look? +Cc: linux-ppc-dev > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > index 0e4270e20fad..4cc8175f9ffd 100644 > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -989,7 +989,7 @@ int add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages, > * addressable memory can force device drivers to use bounce buffers > * and impact their performance negatively: > */ > - if (!params->pgmap) > + if (!params->pgmap || params->pgmap->type != MEMORY_DEVICE_PRIVATE) > /* update max_pfn, max_low_pfn and high_memory */ > update_end_of_memory_vars(start_pfn << PAGE_SHIFT, nr_pages << PAGE_SHIFT); > This looks better to me. ~Gregory