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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> 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: <692e1297e3b6_261c110064@dwillia2-mobl4.notmuch> 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