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From: Lukas Bulwahn <lukas.bulwahn@gmail.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	X86 ML <x86@kernel.org>, Randy Dunlap <rdunlap@infradead.org>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Darren Hart <dvhart@infradead.org>,
	Andy Shevchenko <andy@infradead.org>,
	Lubomir Rintel <lkundrak@v3.sk>, Pavel Machek <pavel@ucw.cz>,
	Lee Jones <lee.jones@linaro.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	platform-driver-x86@vger.kernel.org,
	kernel-janitors <kernel-janitors@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH 0/9] Kconfig symbol clean-up on ./arch/x86/
Date: Tue, 3 Aug 2021 17:12:47 +0200	[thread overview]
Message-ID: <CAKXUXMxQ83T7beOTuZ928=-eo2Tsr94TGxsaYh3+MHOJrDO8Bg@mail.gmail.com> (raw)
In-Reply-To: <f9074e8d-9314-9d7d-7bf5-5b5538c8be8d@intel.com>

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

  reply	other threads:[~2021-08-03 15:13 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03 11:35 Lukas Bulwahn
2021-08-03 11:35 ` [PATCH 1/9] x86/entry: correct reference to intended CONFIG_64_BIT Lukas Bulwahn
2021-10-05 10:32   ` [tip: x86/urgent] x86/entry: Correct " tip-bot2 for Lukas Bulwahn
2021-10-06 17:38   ` tip-bot2 for Lukas Bulwahn
2021-08-03 11:35 ` [PATCH 2/9] x86, olpc: correct condition to intended CONFIG_OLPC_XO15_SCI Lukas Bulwahn
2021-10-05 22:52   ` [tip: x86/urgent] x86/platform/olpc: Correct ifdef symbol " tip-bot2 for Lukas Bulwahn
2021-10-06 17:38   ` tip-bot2 for Lukas Bulwahn
2021-08-03 11:35 ` [PATCH 3/9] x86/Kconfig: correct reference to MWINCHIP3D Lukas Bulwahn
2021-10-05 22:52   ` [tip: x86/urgent] x86/Kconfig: Correct " tip-bot2 for Lukas Bulwahn
2021-10-06 17:38   ` tip-bot2 for Lukas Bulwahn
2021-08-03 11:35 ` [PATCH 4/9] x86/Kconfig: remove reference to obsolete MFD_INTEL_MSIC config Lukas Bulwahn
2021-10-06 14:06   ` [tip: x86/cleanups] x86/Kconfig: Remove references to obsolete Kconfig symbols tip-bot2 for Lukas Bulwahn
2021-08-03 11:35 ` [PATCH 5/9] x86/Kconfig: remove reference to obsolete APB_TIMER config Lukas Bulwahn
2021-10-05 19:57   ` Borislav Petkov
2021-08-03 11:35 ` [PATCH 6/9] x86/irq: fix slightly wrong reference in comment Lukas Bulwahn
2021-10-06 14:06   ` [tip: x86/cleanups] x86: Fix misspelled Kconfig symbols tip-bot2 for Lukas Bulwahn
2021-08-03 11:35 ` [PATCH 7/9] x86/uaccess: adjust comment for endif of CONFIG_CC_HAS_ASM_GOTO_OUTPUT Lukas Bulwahn
2021-08-03 11:35 ` [PATCH 8/9] x86: page_32.h: adjust comment for endif of CONFIG_X86_USE_3DNOW Lukas Bulwahn
2021-08-03 11:35 ` [PATCH 9/9] x86: ia32.h: adjust comment for endif of CONFIG_IA32_EMULATION Lukas Bulwahn
2021-10-05 19:59   ` Borislav Petkov
2021-08-03 14:32 ` [PATCH 0/9] Kconfig symbol clean-up on ./arch/x86/ Dave Hansen
2021-08-03 15:12   ` Lukas Bulwahn [this message]
2021-08-03 15:40     ` Dave Hansen
2021-12-22 13:00       ` Lukas Bulwahn
2021-08-03 21:49 ` Randy Dunlap

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