[PATCH] x86/mce: Need to let kill_proc() send signal to doomedprocess

[Tony Luck]

In commit dad1743e5993f19b3d7e7bd0fb35dc45b5326626
  x86/mce: Only restart instruction after machine check recovery if it is safe

we fixed mce_notify_process() to force a signal to the current process
if it was not restartable (RIPV bit not set in MCG_STATUS). But doing
it here means that the process doesn't get told the virtual address of
the fault via siginfo_t->si_addr. This would prevent application level
recovery from the fault.

Make a new MF_MUST_KILL flag bit for memory_failure() et. al. to use
so that we will provide the right information with the signal.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---

v2: Fix brainfart where I forgot to check mi->restartable to decide whether
    to pass in the new MF_MUST_KILL bit [Thanks Boris for spotting this!]
    Use same style syntax !!(flags & MF_MUST_KILL) [Also from Boris]
    Faked tests with RIPV set and not set ... and found that we need one
    more check on MF_MUST_KILL earlier in hwpoison_user_mappings() to
    make sure it doesn't think the clean page case is recoverable.

 arch/x86/kernel/cpu/mcheck/mce.c |  6 ++++--
 include/linux/mm.h               |  1 +
 mm/memory-failure.c              | 10 ++++++----
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index da27c5d..9f9ed4f 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1186,6 +1186,7 @@ void mce_notify_process(void)
 {
 	unsigned long pfn;
 	struct mce_info *mi = mce_find_info();
+	int flags = MF_ACTION_REQUIRED;
 
 	if (!mi)
 		mce_panic("Lost physical address for unconsumed uncorrectable error", NULL, NULL);
@@ -1200,8 +1201,9 @@ void mce_notify_process(void)
 	 * doomed. We still need to mark the page as poisoned and alert any
 	 * other users of the page.
 	 */
-	if (memory_failure(pfn, MCE_VECTOR, MF_ACTION_REQUIRED) < 0 ||
-			   mi->restartable == 0) {
+	if (mi->restartable == 0)
+		flags |= MF_MUST_KILL;
+	if (memory_failure(pfn, MCE_VECTOR, flags) < 0) {
 		pr_err("Memory error not recovered");
 		force_sig(SIGBUS, current);
 	}
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b36d08c..f9f279c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1591,6 +1591,7 @@ void vmemmap_populate_print_last(void);
 enum mf_flags {
 	MF_COUNT_INCREASED = 1 << 0,
 	MF_ACTION_REQUIRED = 1 << 1,
+	MF_MUST_KILL = 1 << 2,
 };
 extern int memory_failure(unsigned long pfn, int trapno, int flags);
 extern void memory_failure_queue(unsigned long pfn, int trapno, int flags);
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index ab1e714..83cc9ef 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -858,7 +858,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	struct address_space *mapping;
 	LIST_HEAD(tokill);
 	int ret;
-	int kill = 1;
+	int kill = 1, doit;
 	struct page *hpage = compound_head(p);
 	struct page *ppage;
 
@@ -888,7 +888,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	 * be called inside page lock (it's recommended but not enforced).
 	 */
 	mapping = page_mapping(hpage);
-	if (!PageDirty(hpage) && mapping &&
+	if (!(flags & MF_MUST_KILL) && !PageDirty(hpage) && mapping &&
 	    mapping_cap_writeback_dirty(mapping)) {
 		if (page_mkclean(hpage)) {
 			SetPageDirty(hpage);
@@ -965,12 +965,14 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	 * Now that the dirty bit has been propagated to the
 	 * struct page and all unmaps done we can decide if
 	 * killing is needed or not.  Only kill when the page
-	 * was dirty, otherwise the tokill list is merely
+	 * was dirty or the process is not restartable,
+	 * otherwise the tokill list is merely
 	 * freed.  When there was a problem unmapping earlier
 	 * use a more force-full uncatchable kill to prevent
 	 * any accesses to the poisoned memory.
 	 */
-	kill_procs(&tokill, !!PageDirty(ppage), trapno,
+	doit = !!PageDirty(ppage) || !!(flags & MF_MUST_KILL);
+	kill_procs(&tokill, doit, trapno,
 		      ret != SWAP_SUCCESS, p, pfn, flags);
 
 	return ret;
-- 
1.7.10.2.552.gaa3bb87

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