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8eaffa67b4
[Pls also look at https://lkml.org/lkml/2012/2/10/228] Using of PAT to change pages from WB to WC works quite nicely. Changing it back to WB - not so much. The crux of the matter is that the code that does this (__page_change_att_set_clr) has only limited information so when it tries to the change it gets the "raw" unfiltered information instead of the properly filtered one - and the "raw" one tell it that PSE bit is on (while infact it is not). As a result when the PTE is set to be WB from WC, we get tons of: :WARNING: at arch/x86/xen/mmu.c:475 xen_make_pte+0x67/0xa0() :Hardware name: HP xw4400 Workstation .. snip.. :Pid: 27, comm: kswapd0 Tainted: G W 3.2.2-1.fc16.x86_64 #1 :Call Trace: : [<ffffffff8106dd1f>] warn_slowpath_common+0x7f/0xc0 : [<ffffffff8106dd7a>] warn_slowpath_null+0x1a/0x20 : [<ffffffff81005a17>] xen_make_pte+0x67/0xa0 : [<ffffffff810051bd>] __raw_callee_save_xen_make_pte+0x11/0x1e : [<ffffffff81040e15>] ? __change_page_attr_set_clr+0x9d5/0xc00 : [<ffffffff8114c2e8>] ? __purge_vmap_area_lazy+0x158/0x1d0 : [<ffffffff8114cca5>] ? vm_unmap_aliases+0x175/0x190 : [<ffffffff81041168>] change_page_attr_set_clr+0x128/0x4c0 : [<ffffffff81041542>] set_pages_array_wb+0x42/0xa0 : [<ffffffff8100a9b2>] ? check_events+0x12/0x20 : [<ffffffffa0074d4c>] ttm_pages_put+0x1c/0x70 [ttm] : [<ffffffffa0074e98>] ttm_page_pool_free+0xf8/0x180 [ttm] : [<ffffffffa0074f78>] ttm_pool_mm_shrink+0x58/0x90 [ttm] : [<ffffffff8112ba04>] shrink_slab+0x154/0x310 : [<ffffffff8112f17a>] balance_pgdat+0x4fa/0x6c0 : [<ffffffff8112f4b8>] kswapd+0x178/0x3d0 : [<ffffffff815df134>] ? __schedule+0x3d4/0x8c0 : [<ffffffff81090410>] ? remove_wait_queue+0x50/0x50 : [<ffffffff8112f340>] ? balance_pgdat+0x6c0/0x6c0 : [<ffffffff8108fb6c>] kthread+0x8c/0xa0 for every page. The proper fix for this is has been posted and is https://lkml.org/lkml/2012/2/10/228 "x86/cpa: Use pte_attrs instead of pte_flags on CPA/set_p.._wb/wc operations." along with a detailed description of the problem and solution. But since that posting has gone nowhere I am proposing this band-aid solution so that at least users don't get the page corruption (the pages that are WC don't get changed to WB and end up being recycled for filesystem or other things causing mysterious crashes). The negative impact of this patch is that users of WC flag (which are InfiniBand, radeon, nouveau drivers) won't be able to set that flag - so they are going to see performance degradation. But stability is more important here. Fixes RH BZ# 742032, 787403, and 745574 Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> |
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