linux-kernel - Re: [v2 1/1] xen, mm: Allow deferred page initialization for xen pv domains

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Date:   Tue, 27 Feb 2018 08:44:44 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        akataria@...are.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, boris.ostrovsky@...cle.com,
        akpm@...ux-foundation.org, mhocko@...e.com, vbabka@...e.cz,
        luto@...nel.org, labbott@...hat.com,
        kirill.shutemov@...ux.intel.com, bp@...e.de,
        minipli@...glemail.com, jinb.park7@...il.com,
        dan.j.williams@...el.com, bhe@...hat.com,
        zhang.jia@...ux.alibaba.com, mgorman@...hsingularity.net,
        hannes@...xchg.org, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-mm@...ck.org
Subject: Re: [v2 1/1] xen, mm: Allow deferred page initialization for xen pv
 domains

On 26/02/18 17:01, Pavel Tatashin wrote:
> Juergen Gross noticed that commit
> f7f99100d8d ("mm: stop zeroing memory during allocation in vmemmap")
> broke XEN PV domains when deferred struct page initialization is enabled.
> 
> This is because the xen's PagePinned() flag is getting erased from struct
> pages when they are initialized later in boot.
> 
> Juergen fixed this problem by disabling deferred pages on xen pv domains.
> It is desirable, however, to have this feature available as it reduces boot
> time. This fix re-enables the feature for pv-dmains, and fixes the problem
> the following way:
> 
> The fix is to delay setting PagePinned flag until struct pages for all
> allocated memory are initialized, i.e. until after free_all_bootmem().
> 
> A new x86_init.hyper op init_after_bootmem() is called to let xen know
> that boot allocator is done, and hence struct pages for all the allocated
> memory are now initialized. If deferred page initialization is enabled, the
> rest of struct pages are going to be initialized later in boot once
> page_alloc_init_late() is called.
> 
> xen_after_bootmem() walks page table's pages and marks them pinned.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>

Verified to work on a system where the original issue caused a crash.

Reviewed-by: Juergen Gross <jgross@...e.com>
Tested-by: Juergen Gross <jgross@...e.com>


Juergen