linux-kernel - Re: [PATCH 4/5] resource: Report parent to walk_iomem_res

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Date:   Thu, 5 Mar 2020 08:42:34 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dan Williams <dan.j.williams@...el.com>, linux-acpi@...r.kernel.org
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Wei Yang <richardw.yang@...ux.intel.com>, peterz@...radead.org,
        ard.biesheuvel@...aro.org, linux-nvdimm@...ts.01.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] resource: Report parent to walk_iomem_res_desc()
 callback

On 3/2/20 4:20 PM, Dan Williams wrote:
> In support of detecting whether a resource might have been been claimed,
> report the parent to the walk_iomem_res_desc() callback. For example,
> the ACPI HMAT parser publishes "hmem" platform devices per target range.
> However, if the HMAT is disabled / missing a fallback driver can attach
> devices to the raw memory ranges as a fallback if it sees unclaimed /
> orphan "Soft Reserved" resources in the resource tree.
> 
> Otherwise, find_next_iomem_res() returns a resource with garbage data
> from the stack allocation in __walk_iomem_res_desc() for the res->parent
> field.

Just wondering if we shouldn't just copy the complete resource struct and
just override the start and end values? That way, if some code in the
future wants to look at sibling or child values, another change isn't needed.

Just a thought.

Thanks,
Tom

> 
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Wei Yang <richardw.yang@...ux.intel.com>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  kernel/resource.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 76036a41143b..6e22e312fd55 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -386,6 +386,7 @@ static int find_next_iomem_res(resource_size_t start, resource_size_t end,
>  		res->end = min(end, p->end);
>  		res->flags = p->flags;
>  		res->desc = p->desc;
> +		res->parent = p->parent;
>  	}
>  
>  	read_unlock(&resource_lock);
>