From 8eaffa67b43e99ae581622c5133e20b0f48bcef1 Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk Date: Fri, 10 Feb 2012 09:16:27 -0500 Subject: [PATCH] xen/pat: Disable PAT support for now. [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: : [] warn_slowpath_common+0x7f/0xc0 : [] warn_slowpath_null+0x1a/0x20 : [] xen_make_pte+0x67/0xa0 : [] __raw_callee_save_xen_make_pte+0x11/0x1e : [] ? __change_page_attr_set_clr+0x9d5/0xc00 : [] ? __purge_vmap_area_lazy+0x158/0x1d0 : [] ? vm_unmap_aliases+0x175/0x190 : [] change_page_attr_set_clr+0x128/0x4c0 : [] set_pages_array_wb+0x42/0xa0 : [] ? check_events+0x12/0x20 : [] ttm_pages_put+0x1c/0x70 [ttm] : [] ttm_page_pool_free+0xf8/0x180 [ttm] : [] ttm_pool_mm_shrink+0x58/0x90 [ttm] : [] shrink_slab+0x154/0x310 : [] balance_pgdat+0x4fa/0x6c0 : [] kswapd+0x178/0x3d0 : [] ? __schedule+0x3d4/0x8c0 : [] ? remove_wait_queue+0x50/0x50 : [] ? balance_pgdat+0x6c0/0x6c0 : [] 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 --- arch/x86/xen/enlighten.c | 2 ++ arch/x86/xen/mmu.c | 8 ++++---- 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 7c44e1bf981e..4172af8ceeb3 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -1141,7 +1141,9 @@ asmlinkage void __init xen_start_kernel(void) /* Prevent unwanted bits from being set in PTEs. */ __supported_pte_mask &= ~_PAGE_GLOBAL; +#if 0 if (!xen_initial_domain()) +#endif __supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD); __supported_pte_mask |= _PAGE_IOMAP; diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c index 58a0e46c404d..95c1cf60c669 100644 --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -415,13 +415,13 @@ static pteval_t iomap_pte(pteval_t val) static pteval_t xen_pte_val(pte_t pte) { pteval_t pteval = pte.pte; - +#if 0 /* If this is a WC pte, convert back from Xen WC to Linux WC */ if ((pteval & (_PAGE_PAT | _PAGE_PCD | _PAGE_PWT)) == _PAGE_PAT) { WARN_ON(!pat_enabled); pteval = (pteval & ~_PAGE_PAT) | _PAGE_PWT; } - +#endif if (xen_initial_domain() && (pteval & _PAGE_IOMAP)) return pteval; @@ -463,7 +463,7 @@ void xen_set_pat(u64 pat) static pte_t xen_make_pte(pteval_t pte) { phys_addr_t addr = (pte & PTE_PFN_MASK); - +#if 0 /* If Linux is trying to set a WC pte, then map to the Xen WC. * If _PAGE_PAT is set, then it probably means it is really * _PAGE_PSE, so avoid fiddling with the PAT mapping and hope @@ -476,7 +476,7 @@ static pte_t xen_make_pte(pteval_t pte) if ((pte & (_PAGE_PCD | _PAGE_PWT)) == _PAGE_PWT) pte = (pte & ~(_PAGE_PCD | _PAGE_PWT)) | _PAGE_PAT; } - +#endif /* * Unprivileged domains are allowed to do IOMAPpings for * PCI passthrough, but not map ISA space. The ISA -- 2.20.1