linux-kernel - Re: [PATCH v3 1/2] x86/setup: don't remove E820_TYPE

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Message-ID: <20210113112322.GG1106298@kernel.org>
Date:   Wed, 13 Jan 2021 13:23:22 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Baoquan He <bhe@...hat.com>, Borislav Petkov <bp@...en8.de>,
        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 v3 1/2] x86/setup: don't remove E820_TYPE_RAM for pfn 0

On Wed, Jan 13, 2021 at 09:56:49AM +0100, Oscar Salvador wrote:
> On Mon, Jan 11, 2021 at 09:40:16PM +0200, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@...ux.ibm.com>
> > 
> > The first 4Kb of memory is a BIOS owned area and to avoid its allocation
> > for the kernel it was not listed in e820 tables as memory. As the result,
> > pfn 0 was never recognised by the generic memory management and it is not a
> > part of neither node 0 nor ZONE_DMA.
> 
> So, since it never was added to memblock.memory structs, it was not
> initialized by init_unavailable_mem, right?

Actually it was initialized by init_unavailable_mem() and got zone=0 and
node=0, but the DMA zone started from pfn 1, so pfn 0 was never a part of
ZONE_DMA.
 
> -- 
> Oscar Salvador
> SUSE L3

-- 
Sincerely yours,
Mike.