Messages in this thread | | | From | Lukas Bulwahn <> | Date | Tue, 3 Aug 2021 17:12:47 +0200 | Subject | Re: [PATCH 0/9] Kconfig symbol clean-up on ./arch/x86/ |
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On Tue, Aug 3, 2021 at 4:32 PM Dave Hansen <dave.hansen@intel.com> wrote: > > On 8/3/21 4:35 AM, Lukas Bulwahn wrote: > > - a reference to STRICT_IOMEM in arch/x86/mm/init.c > > unclear to me: which exact config this refers to > > Are you referring to the reference in this comment? > > > + /* > > + * This must follow RAM test, since System RAM is considered a > > + * restricted resource under CONFIG_STRICT_IOMEM. > > + */ > > + if (iomem_is_exclusive(pagenr << PAGE_SHIFT)) { > > + /* Low 1MB bypasses iomem restrictions. */ > > + if (pagenr < 256) > > + return 1; > ... >
Yes, that is what I referred to.
> That came from here: > > > commit a4866aa812518ed1a37d8ea0c881dc946409de94 > > Author: Kees Cook <keescook@chromium.org> > > Date: Wed Apr 5 09:39:08 2017 -0700 > > > > mm: Tighten x86 /dev/mem with zeroing reads > > Which also added this hunk: > > > #ifdef CONFIG_STRICT_DEVMEM > > +static inline int page_is_allowed(unsigned long pfn) > > +{ > > + return devmem_is_allowed(pfn); > > +} > > and talks about CONFIG_STRICT_DEVMEM in the changelog: > > > mm: Tighten x86 /dev/mem with zeroing reads > > > > Under CONFIG_STRICT_DEVMEM, reading System RAM through /dev/mem is > > disallowed. However, on x86, the first 1MB was always allowed for BIOS > ... > > It's a pretty safe guess that STRICT_IOMEM refers to CONFIG_STRICT_DEVMEM.
Thanks, Dave.
If the maintainers consider updates to comments making them consistent with the code as worth being picked, I will turn your analysis into a proper commit message and provide a patch to update that comment.
Lukas
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