Linux Virtualization - Feb 2018 - [v2 1/1] xen, mm: Allow deferred page initialization for xen pv domains

* Pavel Tatashin <pasha.tatashin at oracle.com> 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 at oracle.com>
> ---
>  arch/x86/include/asm/x86_init.h |  2 ++
>  arch/x86/kernel/x86_init.c      |  1 +
>  arch/x86/mm/init_32.c           |  1 +
>  arch/x86/mm/init_64.c           |  1 +
>  arch/x86/xen/mmu_pv.c           | 38
++++++++++++++++++++++++++------------
>  mm/page_alloc.c                 |  4 ----
>  6 files changed, 31 insertions(+), 16 deletions(-)
Acked-by: Ingo Molnar <mingo at kernel.org>

Thanks,

	Ingo