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Howlett" , Vlastimil Babka , Suren Baghdasaryan , Ira Weiny , Nishanth Menon , Heiko =?iso-8859-1?Q?St=FCbner?= , Alexander Sverdlin , "Chester A. Unal" , Sergio Paracuellos , Andreas Larsson Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout Message-ID: References: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Sep 10, 2025 at 03:10:05PM +0200, Linus Walleij wrote: > This is is done so that we can unmap *most* of the kernel > memory but *keep* the VMALLOC area, so that e.g. exceptions > can still execute and save to stack when they occur, and we can > call into the kernel to execute said exceptions. > > This in practice means the area 0xf1000000-0xffffffff > which also includes the high exception vectors that must for > natural reasons also be kept in the mapping. > What we have mapped today (all of the time) is > 0xc0000000-0xffffffff. > > A minimal 256 MB mapping from 0xf0000000-0xffffffff > should be able to cover this. Can I ask where the MMIO (PCI?) window lives?