linux-kernel - Re: [PATCH] mm: ignore nomap memory during mirror init

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aHzjOxg_oPp06blC@kernel.org>
Date: Sun, 20 Jul 2025 15:38:19 +0300
From: Mike Rapoport <rppt@...nel.org>
To: mawupeng <mawupeng1@...wei.com>
Cc: akpm@...ux-foundation.org, ardb@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: ignore nomap memory during mirror init

On Fri, Jul 18, 2025 at 09:37:48AM +0800, mawupeng wrote:
> 
> 
> On 2025/7/17 21:37, Mike Rapoport wrote:
> > On Thu, Jul 17, 2025 at 07:06:52PM +0800, mawupeng wrote:
> >>
> >> On 2025/7/17 18:29, Mike Rapoport wrote:
> >>> On Thu, Jul 17, 2025 at 04:57:23PM +0800, Wupeng Ma wrote:
> >>>> When memory mirroring is enabled, the BIOS may reserve memory regions
> >>>> at the start of the physical address space without the MR flag. This will
> >>>> lead to zone_movable_pfn to be updated to the start of these reserved
> >>>> regions, resulting in subsequent mirrored memory being ignored.
> >>>>
> >>>> Here is the log with efi=debug enabled:
> >>>>   efi:   0x084004000000-0x0842bf37ffff [Conventional|   |  |MR|...|WB|WT|WC|  ]
> >>>>   efi:   0x0842bf380000-0x0842c21effff [Loader Code |   |  |MR|...|WB|WT|WC|  ]
> >>>>   efi:   0x0842c21f0000-0x0847ffffffff [Conventional|   |  |MR|...|WB|WT|WC|  ]
> >>>>   efi:   0x085000000000-0x085fffffffff [Conventional|   |  |  |...|WB|WT|WC|  ]
> >>>> ...
> >>>>   efi:   0x084000000000-0x084003ffffff [Reserved    |   |  |  |...|WB|WT|WC|  ]
> >>>>
> >>>> Since this kind of memory can not be used by kernel. ignore nomap memory to fix
> >>>> this issue.
> >>
> >> Since the first non-mirror pfn of this node is 0x084000000000, then zone_movable_pfn 
> >> for this node will be updated to this. This will lead to Mirror Region 
> >>   - 0x084004000000-0x0842bf37ffff
> >>   - 0x0842bf380000-0x0842c21effff 
> >>   - 0x0842c21f0000-0x0847ffffffff
> >> be seen as non-mirror memory since zone_movable_pfn will be the start_pfn of this node
> >> in adjust_zone_range_for_zone_movable().
> > 
> > What do you mean by "seen as non-mirror memory"?
> 
> It mean these memory range will be add to movable zone.
> 
> > 
> > What is the problem with having movable zone on that node start at
> > 0x084000000000?
> > 
> > Can you post the kernel log up to "Memory: nK/mK available" line for more
> > context?
> 
> Memory: nK/mK available can not see be problem here, since there is nothing wrong
> with the total memory. However this problem can be shown via lsmem --output-all

I didn't ask for that particular line but for *up to that line*.
 
> w/o this patch
> [root@...alhost ~]# lsmem --output-all
> RANGE                                  SIZE  STATE REMOVABLE         BLOCK NODE   ZONES
> 0x0000084000000000-0x00000847ffffffff   32G online       yes   67584-67839    0 Movable
> 0x0000085000000000-0x0000085fffffffff   64G online       yes   68096-68607    0 Movable
> 
> w/ this patch
> [root@...alhost ~]# lsmem --output-all
> RANGE                                  SIZE  STATE REMOVABLE         BLOCK NODE   ZONES
> 0x0000084000000000-0x00000847ffffffff   32G online       yes   8448-8479    0  Normal
> 0x0000085000000000-0x0000085fffffffff   64G online       yes   8512-8575    0 Movable

As I see the problem, you have a problematic firmware that fails to report
memory as mirrored because it reserved for firmware own use. This causes
for non-mirrored memory to appear before mirrored memory. And this breaks
an assumption in find_zone_movable_pfns_for_nodes() that mirrored memory
always has lower addresses than non-mirrored memory and you end up wiht
having all the memory in movable zone.

So to workaround this firmware issue you propose a hack that would skip
NOMAP regions while calculating zone_movable_pfn because your particular
firmware reports the reserved mirrored memory as NOMAP.

Why don't you simply pass "kernelcore=32G" on the command line and you'll
get the same result.

> As shown above, All memory in this node is added to Zone Movable even some range of the memory
> is mirror memory. With this patch, 0x0000084000000000-0x00000847ffffffff will be added to
> zone normal as expected since the MR attribute.

-- 
Sincerely yours,
Mike.