linux-kernel - Re: [PATCH v1 1/3] kernel/resource: make walk_system_ram_res() find all busy IORESOURCE_SYSTEM

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Date:   Tue, 23 Mar 2021 12:25:27 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Keith Busch <keith.busch@...el.com>,
        Michal Hocko <mhocko@...e.com>, Qian Cai <cai@....pw>,
        Oscar Salvador <osalvador@...e.de>,
        Eric Biederman <ebiederm@...ssion.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>, x86@...nel.org,
        kexec@...ts.infradead.org
Subject: Re: [PATCH v1 1/3] kernel/resource: make walk_system_ram_res() find
 all busy IORESOURCE_SYSTEM_RAM resources

On 23.03.21 12:06, Andy Shevchenko wrote:
> On Mon, Mar 22, 2021 at 05:01:58PM +0100, David Hildenbrand wrote:
>> It used to be true that we can have busy system RAM only on the first level
>> in the resourc tree. However, this is no longer holds for driver-managed
>> system RAM (i.e., added via dax/kmem and virtio-mem), which gets added on
>> lower levels.
>>
>> We have two users of walk_system_ram_res(), which currently only
>> consideres the first level:
>> a) kernel/kexec_file.c:kexec_walk_resources() -- We properly skip
>>     IORESOURCE_SYSRAM_DRIVER_MANAGED resources via
>>     locate_mem_hole_callback(), so even after this change, we won't be
>>     placing kexec images onto dax/kmem and virtio-mem added memory. No
>>     change.
>> b) arch/x86/kernel/crash.c:fill_up_crash_elf_data() -- we're currently
>>     not adding relevant ranges to the crash elf info, resulting in them
>>     not getting dumped via kdump.
>>
>> This change fixes loading a crashkernel via kexec_file_load() and including
> 
> "...fixes..." effectively means to me that Fixes tag should be provided.

We can certainly add, although it doesn't really affect the running 
kernel, but only crashdumps taken in the kdump kernel:

Fixes: ebf71552bb0e ("virtio-mem: Add parent resource for all added 
"System RAM"")
Fixes: c221c0b0308f ("device-dax: "Hotplug" persistent memory for use 
like normal RAM")

Thanks

-- 
Thanks,

David / dhildenb