linux-kernel - Re: [PATCH 1/2] x86/setup: consolidate early memory reservations

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Message-ID: <20210125145041.GD23070@zn.tnic>
Date:   Mon, 25 Jan 2021 15:50:41 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Baoquan He <bhe@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>, Qian Cai <cai@....pw>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH 1/2] x86/setup: consolidate early memory reservations

On Fri, Jan 15, 2021 at 10:32:54AM +0200, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> The early reservations of memory areas used by the firmware, bootloader,
> kernel text and data are spread over setup_arch(). Moreover, some of them
> happen *after* memblock allocations, e.g trim_platform_memory_ranges() and
> trim_low_memory_range() are called after reserve_real_mode() that allocates
> memory.
> 
> We did not observe corruption of these memory regions because memblock

Make that "We" impersonal, passive voice pls.

> always allocates memory either from the end of memory (in top-down mode) or
> above the kernel image (in bottom-up mode). However, the bottom up mode is
> going to be updated to span the entire memory [1] to avoid limitations
> caused by KASLR.
> 
> Consolidate early memory reservations in a dedicated function to improve
> robustness against future changes. Having the early reservations in one
> place also makes it clearer what memory must be reserved before we allow
> memblock allocations.

Would it make sense to have a check with a WARN or so to catch early
reservations which get added after memblock allocations have been
allowed? To catch people who don't pay attention...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette