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authorLuckTony <tony.luck@intel.com>2018-08-31 09:55:06 -0700
committerThomas Gleixner <tglx@linutronix.de>2018-09-01 14:59:19 +0200
commitc7486104a5ce7e8763e3cb5157bba8d0f1468d87 (patch)
tree2ee0f08523889787829bf370b0f3566855dd0f01
parenteeb89e2bb1ac45b0836d4170e97a988c3a746c62 (diff)
downloadlinux-stericsson-c7486104a5ce7e8763e3cb5157bba8d0f1468d87.tar.gz
x86/mce: Fix set_mce_nospec() to avoid #GP fault
The trick with flipping bit 63 to avoid loading the address of the 1:1 mapping of the poisoned page while the 1:1 map is updated used to work when unmapping the page. But it falls down horribly when attempting to directly set the page as uncacheable. The problem is that when the cache mode is changed to uncachable, the pages needs to be flushed from the cache first. But the decoy address is non-canonical due to bit 63 flipped, and the CLFLUSH instruction throws a #GP fault. Add code to change_page_attr_set_clr() to fix the address before calling flush. Fixes: 284ce4011ba6 ("x86/memory_failure: Introduce {set, clear}_mce_nospec()") Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Tony Luck <tony.luck@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Anvin <hpa@zytor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: linux-edac <linux-edac@vger.kernel.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Jiang <dave.jiang@intel.com> Link: https://lkml.kernel.org/r/20180831165506.GA9605@agluck-desk
-rw-r--r--arch/x86/mm/pageattr.c25
1 files changed, 24 insertions, 1 deletions
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 8d6c34fe49be..51a5a69ecac9 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1420,6 +1420,29 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
return 0;
}
+/*
+ * Machine check recovery code needs to change cache mode of poisoned
+ * pages to UC to avoid speculative access logging another error. But
+ * passing the address of the 1:1 mapping to set_memory_uc() is a fine
+ * way to encourage a speculative access. So we cheat and flip the top
+ * bit of the address. This works fine for the code that updates the
+ * page tables. But at the end of the process we need to flush the cache
+ * and the non-canonical address causes a #GP fault when used by the
+ * CLFLUSH instruction.
+ *
+ * But in the common case we already have a canonical address. This code
+ * will fix the top bit if needed and is a no-op otherwise.
+ */
+static inline unsigned long make_addr_canonical_again(unsigned long addr)
+{
+#ifdef CONFIG_X86_64
+ return (long)(addr << 1) >> 1;
+#else
+ return addr;
+#endif
+}
+
+
static int change_page_attr_set_clr(unsigned long *addr, int numpages,
pgprot_t mask_set, pgprot_t mask_clr,
int force_split, int in_flag,
@@ -1465,7 +1488,7 @@ static int change_page_attr_set_clr(unsigned long *addr, int numpages,
* Save address for cache flush. *addr is modified in the call
* to __change_page_attr_set_clr() below.
*/
- baddr = *addr;
+ baddr = make_addr_canonical_again(*addr);
}
/* Must avoid aliasing mappings in the highmem code */