Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751144AbdFPUJq (ORCPT ); Fri, 16 Jun 2017 16:09:46 -0400 Received: from mga01.intel.com ([192.55.52.88]:21679 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750879AbdFPUJp (ORCPT ); Fri, 16 Jun 2017 16:09:45 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.39,348,1493708400"; d="scan'208";a="868801413" From: "Luck, Tony" To: Borislav Petkov Cc: Tony Luck , Dave Hansen , Naoya Horiguchi , x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH] mm/hwpoison: Clear PRESENT bit for kernel 1:1 mappings of poison pages Date: Fri, 16 Jun 2017 12:02:00 -0700 Message-Id: <20170616190200.6210-1-tony.luck@intel.com> X-Mailer: git-send-email 2.11.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4233 Lines: 128 From: Tony Luck Speculative processor accesses may reference any memory that has a valid page table entry. While a speculative access won't generate a machine check, it will log the error in a machine check bank. That could cause escalation of a subsequent error since the overflow bit will be then set in the machine check bank status register. Code has to be double-plus-tricky to avoid mentioning the 1:1 virtual address of the page we want to map out otherwise we may trigger the very problem we are trying to avoid. We use a non-canonical address that passes through the usual Linux table walking code to get to the same "pte". Cc: Dave Hansen Cc: Naoya Horiguchi Cc: x86@kernel.org Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Tony Luck --- Thanks to Dave Hansen for reviewing several iterations of this. arch/x86/include/asm/page_64.h | 4 ++++ arch/x86/kernel/cpu/mcheck/mce.c | 35 +++++++++++++++++++++++++++++++++++ include/linux/mm_inline.h | 6 ++++++ mm/memory-failure.c | 2 ++ 4 files changed, 47 insertions(+) diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h index b4a0d43248cf..b50df06ad251 100644 --- a/arch/x86/include/asm/page_64.h +++ b/arch/x86/include/asm/page_64.h @@ -51,6 +51,10 @@ static inline void clear_page(void *page) void copy_page(void *to, void *from); +#ifdef CONFIG_X86_MCE +#define arch_unmap_kpfn arch_unmap_kpfn +#endif + #endif /* !__ASSEMBLY__ */ #ifdef CONFIG_X86_VSYSCALL_EMULATION diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index 5cfbaeb6529a..56563db0b2be 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -51,6 +51,7 @@ #include #include #include +#include #include "mce-internal.h" @@ -1056,6 +1057,40 @@ static int do_memory_failure(struct mce *m) return ret; } +#ifdef CONFIG_X86_64 + +void arch_unmap_kpfn(unsigned long pfn) +{ + unsigned long decoy_addr; + + /* + * Unmap this page from the kernel 1:1 mappings to make sure + * we don't log more errors because of speculative access to + * the page. + * We would like to just call: + * set_memory_np((unsigned long)pfn_to_kaddr(pfn), 1); + * but doing that would radically increase the odds of a + * speculative access to the posion page because we'd have + * the virtual address of the kernel 1:1 mapping sitting + * around in registers. + * Instead we get tricky. We create a non-canonical address + * that looks just like the one we want, but has bit 63 flipped. + * This relies on set_memory_np() not checking whether we passed + * a legal address. + */ + +#if PGDIR_SHIFT + 9 < 63 /* 9 because cpp doesn't grok ilog2(PTRS_PER_PGD) */ + decoy_addr = (pfn << PAGE_SHIFT) + (PAGE_OFFSET ^ BIT(63)); +#else +#error "no unused virtual bit available" +#endif + + if (set_memory_np(decoy_addr, 1)) + pr_warn("Could not invalidate pfn=0x%lx from 1:1 map \n", pfn); + +} +#endif + /* * The actual machine check handler. This only handles real * exceptions when something got corrupted coming in through int 18. diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index e030a68ead7e..25438b2b6f22 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -126,4 +126,10 @@ static __always_inline enum lru_list page_lru(struct page *page) #define lru_to_page(head) (list_entry((head)->prev, struct page, lru)) +#ifdef arch_unmap_kpfn +extern void arch_unmap_kpfn(unsigned long pfn); +#else +static __always_inline void arch_unmap_kpfn(unsigned long pfn) { } +#endif + #endif diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 342fac9ba89b..9479e190dcbd 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1071,6 +1071,8 @@ int memory_failure(unsigned long pfn, int trapno, int flags) return 0; } + arch_unmap_kpfn(pfn); + /* * Currently errors on hugetlbfs pages are measured in hugepage units, * so nr_pages should be 1 << compound_order. OTOH when errors are on -- 2.11.0