linux-kernel - Re: [PATCH v5 2/7] mm, devm_memremap_pages: Kill mapping "System RAM" support

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Message-ID: <20180918202818.GB14689@redhat.com>
Date:   Tue, 18 Sep 2018 16:28:19 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     akpm@...ux-foundation.org, Christoph Hellwig <hch@....de>,
        Logan Gunthorpe <logang@...tatee.com>,
        alexander.h.duyck@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/7] mm, devm_memremap_pages: Kill mapping "System
 RAM" support

On Wed, Sep 12, 2018 at 07:22:11PM -0700, Dan Williams wrote:
> Given the fact that devm_memremap_pages() requires a percpu_ref that is
> torn down by devm_memremap_pages_release() the current support for
> mapping RAM is broken.
> 
> Support for remapping "System RAM" has been broken since the beginning
> and there is no existing user of this this code path, so just kill the
> support and make it an explicit error.
> 
> This cleanup also simplifies a follow-on patch to fix the error path
> when setting a devm release action for devm_memremap_pages_release()
> fails.
> 
> Cc: Christoph Hellwig <hch@....de>

Reviewed-by: Jérôme Glisse <jglisse@...hat.com>

> Cc: Logan Gunthorpe <logang@...tatee.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  kernel/memremap.c |    9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index f95c7833db6d..92e838127767 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -202,15 +202,12 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
>  	is_ram = region_intersects(align_start, align_size,
>  		IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE);
>  
> -	if (is_ram == REGION_MIXED) {
> -		WARN_ONCE(1, "%s attempted on mixed region %pr\n",
> -				__func__, res);
> +	if (is_ram != REGION_DISJOINT) {
> +		WARN_ONCE(1, "%s attempted on %s region %pr\n", __func__,
> +				is_ram == REGION_MIXED ? "mixed" : "ram", res);
>  		return ERR_PTR(-ENXIO);
>  	}
>  
> -	if (is_ram == REGION_INTERSECTS)
> -		return __va(res->start);
> -
>  	if (!pgmap->ref)
>  		return ERR_PTR(-EINVAL);
>  
>