linux-kernel - Re: [PATCH] mm: don't defer struct page initialization for Xen pv guests

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Message-ID: <20180216135940.GQ7275@dhcp22.suse.cz>
Date:   Fri, 16 Feb 2018 14:59:40 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        xen-devel@...ts.xenproject.org, akpm@...ux-foundation.org,
        stable@...r.kernel.org, Pavel Tatashin <pasha.tatashin@...cle.com>
Subject: Re: [PATCH] mm: don't defer struct page initialization for Xen pv
 guests

[CC Pavel]

On Fri 16-02-18 14:37:26, Juergen Gross wrote:
> Commit f7f99100d8d95dbcf09e0216a143211e79418b9f ("mm: stop zeroing
> memory during allocation in vmemmap") broke Xen pv domains in some
> configurations, as the "Pinned" information in struct page of early
> page tables could get lost.

Could you be more specific please?

> Avoid this problem by not deferring struct page initialization when
> running as Xen pv guest.
> 
> Cc: <stable@...r.kernel.org> #4.15
Fixes: f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap")

please

> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  mm/page_alloc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 81e18ceef579..681d504b9a40 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -347,6 +347,9 @@ static inline bool update_defer_init(pg_data_t *pgdat,
>  	/* Always populate low zones for address-constrained allocations */
>  	if (zone_end < pgdat_end_pfn(pgdat))
>  		return true;
> +	/* Xen PV domains need page structures early */
> +	if (xen_pv_domain())
> +		return true;
>  	(*nr_initialised)++;
>  	if ((*nr_initialised > pgdat->static_init_pgcnt) &&
>  	    (pfn & (PAGES_PER_SECTION - 1)) == 0) {
> -- 
> 2.13.6

-- 
Michal Hocko
SUSE Labs