From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Vlastimil Babka <vbabka@suse.cz>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range
Date: Fri, 26 Mar 2021 15:53:41 +0100 [thread overview]
Message-ID: <0e735ea7-b3d9-615e-6bba-fa3a16883226@redhat.com> (raw)
In-Reply-To: <YF3x8BW1+2o50mds@dhcp22.suse.cz>
On 26.03.21 15:38, Michal Hocko wrote:
> On Fri 26-03-21 09:52:58, David Hildenbrand wrote:
> [...]
>> Something else to note:
>>
>>
>> We'll not call the memory notifier (e.g., MEM_ONLINE) for the vmemmap. The
>> result is that
>>
>> 1. We won't allocate extended struct pages for the range. Don't think this
>> is really problematic (pages are never allocated/freed, so I guess we don't
>> care - like ZONE_DEVICE code).
>
> Agreed. I do not think we need them. Future might disagree but let's
> handle it when we have a clear demand.
>
>> 2. We won't allocate kasan shadow memory. We most probably have to do it
>> explicitly via kasan_add_zero_shadow()/kasan_remove_zero_shadow(), see
>> mm/memremap.c:pagemap_range()
>
> I think this is similar to the above. Does kasan has to know about
> memory which will never be used for anything?
IIRC, kasan will track read/writes to the vmemmap as well. So it could
theoretically detect if we read from the vmemmap before writing
(initializing) it IIUC.
This is also why mm/memremap.c does a kasan_add_zero_shadow() before the
move_pfn_range_to_zone()->memmap_init_range() for the whole region,
including altmap space.
Now, I am no expert on KASAN, what would happen in case we have access
to non-tracked memory.
commit 0207df4fa1a869281ddbf72db6203dbf036b3e1a
Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Date: Fri Aug 17 15:47:04 2018 -0700
kernel/memremap, kasan: make ZONE_DEVICE with work with KASAN
indicates that kasan will crash the system on "non-existent shadow memory"
>
>> Further a locking rework might be necessary. We hold the device hotplug
>> lock, but not the memory hotplug lock. E.g., for get_online_mems(). Might
>> have to move that out online_pages.
>
> Could you be more explicit why this locking is needed? What it would
> protect from for vmemmap pages?
>
One example is in mm/kmemleak.c:kmemleak_scan(), where we scan the
vmemmap for pointers. We don't want the vmemmap to get unmapped while we
are working on it (-> fault).
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-03-26 14:53 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-19 9:26 [PATCH v5 0/5] Allocate memmap from hotadded memory (per device) Oscar Salvador
2021-03-19 9:26 ` [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range Oscar Salvador
2021-03-19 10:20 ` David Hildenbrand
2021-03-19 10:31 ` Oscar Salvador
2021-03-19 12:04 ` David Hildenbrand
2021-03-23 10:11 ` Michal Hocko
2021-03-24 10:12 ` Oscar Salvador
2021-03-24 12:03 ` Michal Hocko
2021-03-24 12:10 ` Michal Hocko
2021-03-24 12:23 ` David Hildenbrand
2021-03-24 12:37 ` Michal Hocko
2021-03-24 13:13 ` David Hildenbrand
2021-03-24 13:40 ` Michal Hocko
2021-03-24 14:05 ` David Hildenbrand
2021-03-24 13:27 ` Oscar Salvador
2021-03-24 14:42 ` Michal Hocko
2021-03-24 14:52 ` David Hildenbrand
2021-03-24 16:04 ` Michal Hocko
2021-03-24 19:16 ` David Hildenbrand
2021-03-25 8:07 ` Oscar Salvador
2021-03-25 9:17 ` Michal Hocko
2021-03-25 10:55 ` Oscar Salvador
2021-03-25 11:08 ` David Hildenbrand
2021-03-25 11:23 ` Oscar Salvador
2021-03-25 12:35 ` Michal Hocko
2021-03-25 12:40 ` David Hildenbrand
2021-03-25 14:08 ` Michal Hocko
2021-03-25 14:09 ` David Hildenbrand
2021-03-25 14:34 ` Michal Hocko
2021-03-25 14:46 ` David Hildenbrand
2021-03-25 15:12 ` Michal Hocko
2021-03-25 15:19 ` David Hildenbrand
2021-03-25 15:35 ` Michal Hocko
2021-03-25 15:40 ` David Hildenbrand
2021-03-25 16:07 ` Michal Hocko
2021-03-25 16:20 ` David Hildenbrand
2021-03-25 16:36 ` Michal Hocko
2021-03-25 16:47 ` Michal Hocko
2021-03-25 16:55 ` David Hildenbrand
2021-03-25 22:06 ` Oscar Salvador
2021-03-26 8:35 ` Michal Hocko
2021-03-26 8:52 ` David Hildenbrand
2021-03-26 8:57 ` Oscar Salvador
2021-03-26 12:15 ` Oscar Salvador
2021-03-26 13:36 ` David Hildenbrand
2021-03-26 14:38 ` Michal Hocko
2021-03-26 14:53 ` David Hildenbrand [this message]
2021-03-26 15:31 ` Michal Hocko
2021-03-26 16:03 ` David Hildenbrand
2021-03-26 8:55 ` Oscar Salvador
2021-03-26 9:11 ` Michal Hocko
2021-03-25 18:08 ` David Hildenbrand
2021-03-25 12:26 ` Michal Hocko
2021-03-25 14:02 ` Oscar Salvador
2021-03-25 14:40 ` Michal Hocko
2021-03-19 9:26 ` [PATCH v5 2/5] acpi,memhotplug: Enable MHP_MEMMAP_ON_MEMORY when supported Oscar Salvador
2021-03-23 10:40 ` Michal Hocko
2021-03-19 9:26 ` [PATCH v5 3/5] mm,memory_hotplug: Add kernel boot option to enable memmap_on_memory Oscar Salvador
2021-03-23 10:47 ` Michal Hocko
2021-03-24 8:45 ` Oscar Salvador
2021-03-24 9:02 ` Michal Hocko
2021-03-19 9:26 ` [PATCH v5 4/5] x86/Kconfig: Introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE Oscar Salvador
2021-03-19 9:26 ` [PATCH v5 5/5] arm64/Kconfig: " Oscar Salvador
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