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Date:   Thu, 28 Jan 2021 11:35:41 +0200
From:   Mike Rapoport <rppt@linux.ibm.com>
To:     Andreas Larsson <andreas@gaisler.com>
Cc:     Sparc kernel list <sparclinux@vger.kernel.org>, linux-mm@kvack.org,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Sam Ravnborg <sam@ravnborg.org>,
        Michal Hocko <mhocko@kernel.org>
Subject: Re: sparc32: boot fails with > 256 MB memory after switch to
 NO_BOOTMEM
Message-ID: <20210128093541.GC299309@linux.ibm.com>
References: <5adb7c41-ad71-b904-6b73-35aef4dfcafe@gaisler.com>
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On Wed, Jan 27, 2021 at 04:03:00PM +0100, Andreas Larsson wrote:
> 
> 
> Commit cca079ef8ac29a7c02192d2bad2ffe4c0c5ffdd0 makes sparc32 use
> memblocks instead of the previous bootmem solution. Unfortunately, due
> to this:
> 
> #define PAGE_OFFSET  0xf0000000
> #define __va(x)	     ((void *)((unsigned long) (x) - phys_base +
> PAGE_OFFSET))
> #define phys_to_virt __va
> 
> it makes physical addresses >= 0x10000000 past phys_base wrap around the
> 32-bit memory space when converted to virtual addresses, e.g. in
> memblock_alloc_try_nid. Physical memory exactly 0x10000000 past
> phys_base is returned as an unintended NULL pointer, leading to a panic
> in my boot when percpu memory allocation fails due to it.
> 
> Unfortunately I have had 256 MB memory or less in a lot of my testing,
> so this old one has slipped by me.
> 
> Does anyone has any ideas or pointers on how to resolve this?

I think the simplest way to work around this is to limit early allocations
to 256M with addition of

	memblock_set_current_limit(SZ_256M);
 
somewhere at setup_arch().

The page allocator will anyway see the entire memory, so I cannot think of
any downside here.

> Example follows where I have 512 MB memory at 0x40000000:
> 
> ----->%>%>%>%-----
> memblock_add: [0x40000000-0x5fffafff] bootmem_init+0x1f8/0x210
> 319MB HIGHMEM available.
> memblock_reserve: [0x40000000-0x40e71fff] bootmem_init+0x178/0x210
> memblock_add: [0x40000000-0x40e71fff] bootmem_init+0x188/0x210
> memblock_alloc_try_nid: 5242880 bytes align=0x40000 nid=-1 from=0x00000000
> max_addr=0x00000000 srmmu_nocache_init+0x20/0x25c
> memblock_reserve: [0x40e80000-0x4137ffff]
> memblock_alloc_range_nid+0xcc/0x178
> memblock_alloc_try_nid: 2560 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 srmmu_nocache_init+0x94/0x25c
> memblock_reserve: [0x40e72000-0x40e729ff]
> memblock_alloc_range_nid+0xcc/0x178
> memblock_alloc_try_nid: 4096 bytes align=0x20 nid=-1 from=0x00000000
> max_addr=0x00000000 sparc_context_init+0x1c/0xe4
> memblock_reserve: [0x40e72a00-0x40e739ff]
> memblock_alloc_range_nid+0xcc/0x178
> Zone ranges:
>   DMA      [mem 0x0000000040000000-0x000000004bffffff]
>   Normal   empty
>   HighMem  [mem 0x000000004c000000-0x000000005fffafff]
> Movable zone start for each node
> Early memory node ranges
>   node   0: [mem 0x0000000040000000-0x000000005fffafff]
> Initmem setup node 0 [mem 0x0000000040000000-0x000000005fffafff]
> ----->%>%>%>%-----
> 
> then much much later memblock_alloc_internal gets 0x50000000 from
> memblock_alloc_range_nid and returns a NULL pointer as result of
> phys_to_virt.
> 
> ----->%>%>%>%-----
> memblock_alloc_try_nid: 40960 bytes align=0x1000 nid=-1 from=0x4fffffff
> max_addr=0x00000000 pcpu_dfl_fc_alloc+0x28/0x40
> memblock_reserve: [0x50000000-0x50009fff]
> memblock_alloc_range_nid+0xcc/0x178
> memblock_free: [0x40e7e000-0x40e7efff] pcpu_free_alloc_info+0x1c/0x30
> memblock_free: [0x40e7f000-0x40e7ffff] pcpu_embed_first_chunk+0x194/0x3b8
> Kernel panic - not syncing: Failed to initialize percpu areas.
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.11.0-rc3-00040-gbc4547251e1-dirty
> #28
> ----->%>%>%>%-----
> 
> Adding mem=256M to the command line solves the panic problem but makes
> the extra memory not be available for normal allocation later on either.
> 
> The two first memblock_add calls (seen in the first first set of
> outputs) with overlapping address ranges that is done in bootmem_init
> also looks a bit worrying, but removing the second one does not affect
> this problem.
> 
> -- 
> Best regards,
> 
> Andreas Larsson
> Cobham Gaisler

-- 
Sincerely yours,
Mike.