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Date: Wed, 10 Sep 2025 15:04:54 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>, ksummit@lists.linux.dev,
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Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout
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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?