Re: [PATCH 2/3] mm/memory_hotplug: Allow arch override of non boot memory resource names

From: David Hildenbrand <david@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>,
	James Morse <james.morse@arm.com>
Cc: kexec@lists.infradead.org, linux-mm@kvack.org,
	linux-arm-kernel@lists.infradead.org,
	Eric Biederman <ebiederm@xmission.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Bhupesh Sharma <bhsharma@redhat.com>
Subject: Re: [PATCH 2/3] mm/memory_hotplug: Allow arch override of non boot memory resource names
Date: Mon, 11 May 2020 10:35:01 +0200	[thread overview]
Message-ID: <f4aa1ac4-5878-0f9d-d94c-cdecc5d4ce18@redhat.com> (raw)
In-Reply-To: <20200508174536.77c7aa3d5d0220cedd07f2e9@linux-foundation.org>

On 09.05.20 02:45, Andrew Morton wrote:
> On Thu, 26 Mar 2020 18:07:29 +0000 James Morse <james.morse@arm.com> wrote:
> 
>> Memory added to the system by hotplug has a 'System RAM' resource created
>> for it. This is exposed to user-space via /proc/iomem.
>>
>> This poses problems for kexec on arm64. If kexec decides to place the
>> kernel in one of these newly onlined regions, the new kernel will find
>> itself booting from a region not described as memory in the firmware
>> tables.
>>
>> Arm64 doesn't have a structure like the e820 memory map that can be
>> re-written when memory is brought online. Instead arm64 uses the UEFI
>> memory map, or the memory node from the DT, sometimes both. We never
>> rewrite these.
>>
>> Allow an architecture to specify a different name for these hotplug
>> regions.
>>
>> ...
>>
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -42,6 +42,10 @@
>>  #include "internal.h"
>>  #include "shuffle.h"
>>  
>> +#ifndef MEMORY_HOTPLUG_RES_NAME
>> +#define MEMORY_HOTPLUG_RES_NAME "System RAM"
>> +#endif
>> +
>>  /*
>>   * online_page_callback contains pointer to current page onlining function.
>>   * Initially it is generic_online_page(). If it is required it could be
>> @@ -103,7 +107,7 @@ static struct resource *register_memory_resource(u64 start, u64 size)
>>  {
>>  	struct resource *res;
>>  	unsigned long flags =  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>> -	char *resource_name = "System RAM";
>> +	char *resource_name = MEMORY_HOTPLUG_RES_NAME;
>>  
>>  	if (start + size > max_mem_size)
>>  		return ERR_PTR(-E2BIG);
> 
> I suppose we should do this as well:
> 
> --- a/mm/memory_hotplug.c~mm-memory_hotplug-allow-arch-override-of-non-boot-memory-resource-names-fix
> +++ a/mm/memory_hotplug.c
> @@ -129,7 +129,8 @@ static struct resource *register_memory_
>  			       resource_name, flags);
>  
>  	if (!res) {
> -		pr_debug("Unable to reserve System RAM region: %016llx->%016llx\n",
> +		pr_debug("Unable to reserve " MEMORY_HOTPLUG_RES_NAME
> +				" region: %016llx->%016llx\n",
>  				start, start + size);
>  		return ERR_PTR(-EEXIST);
>  	}
> 
> It assumes that MEMORY_HOTPLUG_RES_NAME will be a literal string, which
> is the case in [3/3].

@Andrew, as discussed in this thread already [1], I suggest to drop this
series from -mm tree for now.

[1] https://lkml.kernel.org/r/2e3419b2-d00c-51c3-9b45-9de114608cdf@arm.com

-- 
Thanks,

David / dhildenb