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

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Date:   Wed, 24 Mar 2021 12:18:40 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     David Hildenbrand <david@...hat.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>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        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>,
        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 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.

Let me ask some rookie questions:

What does "busy" term stand for here?
Why resources coming from virtio-mem are added at a 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
> dax/kmem and virtio-mem added System RAM in the crashdump on x86-64. Note
> that e.g,, arm64 relies on memblock data and, therefore, always considers
> all added System RAM already.
> 
> Let's find all busy IORESOURCE_SYSTEM_RAM resources, making the function
> behave like walk_system_ram_range().
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> Cc: Signed-off-by: David Hildenbrand <david@...hat.com>
> Cc: Dave Young <dyoung@...hat.com>
> Cc: Baoquan He <bhe@...hat.com>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Keith Busch <keith.busch@...el.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Qian Cai <cai@....pw>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Brijesh Singh <brijesh.singh@....com>
> Cc: x86@...nel.org
> Cc: kexec@...ts.infradead.org
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  kernel/resource.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 627e61b0c124..4efd6e912279 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -457,7 +457,7 @@ int walk_system_ram_res(u64 start, u64 end, void *arg,
>  {
>  	unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>  
> -	return __walk_iomem_res_desc(start, end, flags, IORES_DESC_NONE, true,
> +	return __walk_iomem_res_desc(start, end, flags, IORES_DESC_NONE, false,
>  				     arg, func);
>  }
>  
> -- 
> 2.29.2
> 
> 

-- 
Oscar Salvador
SUSE L3