linux-kernel - Re: [RFC][PATCH] kexec: Teach indirect pages how to live in high memory

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Date:   Fri, 9 Oct 2020 10:35:12 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Hari Bathini <hbathini@...ux.ibm.com>, kernel-team@....com,
        Michal Hocko <mhocko@...e.com>,
        Minchan Kim <minchan@...nel.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Rik van Riel <riel@...riel.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Christian Koenig <christian.koenig@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Huang Rui <ray.huang@....com>,
        Kexec Mailing List <kexec@...ts.infradead.org>,
        Pavel Machek <pavel@....cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Laura Abbott <labbott@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [RFC][PATCH] kexec: Teach indirect pages how to live in high
 memory

On Tue, May 05, 2020 at 01:39:16PM -0500, Eric W. Biederman wrote:
> Hari Bathini <hbathini@...ux.ibm.com> writes:
> 
> > On 05/05/20 3:29 am, Eric W. Biederman wrote:
> >> 
> >> Recently a patch was proposed to kimage_alloc_page to slightly alter
> >> the logic of how pages allocated with incompatible flags were
> >> detected.  The logic was being altered because the semantics of the
> >> page alloctor were changing yet again.
> >> 
> >> Looking at that case I realized that there is no reason for it to even
> >> exist.  Either the indirect page allocations and the source page
> >> allocations could be separated out, or I could do as I am doing now
> >> and simply teach the indirect pages to live in high memory.
> >> 
> >> This patch replaced pointers of type kimage_entry_t * with a new type
> >> kimage_entry_pos_t.  This new type holds the physical address of the
> >> indirect page and the offset within that page of the next indirect
> >> entry to write.  A special constant KIMAGE_ENTRY_POS_INVALID is added
> >> that kimage_image_pos_t variables that don't currently have a valid
> >> may be set to.
> >> 
> >> Two new functions kimage_read_entry and kimage_write_entry have been
> >> provided to write entries in way that works if they live in high
> >> memory.
> >> 
> >> The now unnecessary checks to see if a destination entry is non-zero
> >> and to increment it if so have been removed.  For safety new indrect
> >> pages are now cleared so we have a guarantee everything that has not
> >> been used yet is zero.  Along with this writing an extra trailing 0
> >> entry has been removed, as it is known all trailing entries are now 0.
> >> 
> >> With highmem support implemented for indirect pages
> >> kimage_image_alloc_page has been updated to always allocate
> >> GFP_HIGHUSER pages, and handling of pages with different
> >> gfp flags has been removed.
> >> 
> >> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> >
> > Eric, the patch failed with data access exception on ppc64. Using the below patch on top
> > got me going...
> 
> Doh!  Somehow I thought I had put that logic or something equivalent
> into kimage_write_entry and it appears I did not.  I will see if I can
> respin the patch.
> 
> Thank you very much for testing.

Hello, Eric.

It seems that this patch isn't upstreamed.
Could you respin the patch?
I've tested this one on x86_32 (highmem enabled) and it works well.

Thanks.