[PATCH 2/3] mm/memory-failure.c: support reset PTE during unpoison

[zhenwei pi <pizhenwei@bytedance.com>]

Origianlly, unpoison_memory() is only used by hwpoison-inject, and
unpoisons a page which is poisoned by hwpoison-inject too. The kernel PTE
entry has no change during software poison/unpoison.

On a virtualization platform, it's possible to fix hardware corrupted page
by hypervisor, typically the hypervisor remaps the error HVA(host virtual
address). So add a new parameter 'const char *reason' to show the reason
called by.

Once the corrupted page gets fixed, the guest kernel needs put page to
buddy. Reuse the page and hit the following issue(Intel Platinum 8260):
 BUG: unable to handle page fault for address: ffff888061646000
 #PF: supervisor write access in kernel mode
 #PF: error_code(0x0002) - not-present page
 PGD 2c01067 P4D 2c01067 PUD 61aaa063 PMD 10089b063 PTE 800fffff9e9b9062
 Oops: 0002 [#1] PREEMPT SMP NOPTI
 CPU: 2 PID: 31106 Comm: stress Kdump: loaded Tainted: G   M       OE     5.18.0-rc6.bm.1-amd64 #6
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
 RIP: 0010:clear_page_erms+0x7/0x10

The kernel PTE entry of the fixed page is still uncorrected, kernel hits
page fault during prep_new_page. So add 'bool reset_kpte' to get a change
to fix the PTE entry if the page is fixed by hypervisor.

Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
---
 include/linux/mm.h   |  2 +-
 mm/hwpoison-inject.c |  2 +-
 mm/memory-failure.c  | 26 +++++++++++++++++++-------
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 665873c2788c..7ba210e86401 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3191,7 +3191,7 @@ enum mf_flags {
 extern int memory_failure(unsigned long pfn, int flags);
 extern void memory_failure_queue(unsigned long pfn, int flags);
 extern void memory_failure_queue_kick(int cpu);
-extern int unpoison_memory(unsigned long pfn);
+extern int unpoison_memory(unsigned long pfn, bool reset_kpte, const char *reason);
 extern int sysctl_memory_failure_early_kill;
 extern int sysctl_memory_failure_recovery;
 extern void shake_page(struct page *p);
diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
index 5c0cddd81505..0dd17ba98ade 100644
--- a/mm/hwpoison-inject.c
+++ b/mm/hwpoison-inject.c
@@ -57,7 +57,7 @@ static int hwpoison_unpoison(void *data, u64 val)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	return unpoison_memory(val);
+	return unpoison_memory(val, false, "hwpoison-inject");
 }
 
 DEFINE_DEBUGFS_ATTRIBUTE(hwpoison_fops, NULL, hwpoison_inject, "%lli\n");
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 95c218bb0a37..a46de3be1dd7 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2132,21 +2132,26 @@ core_initcall(memory_failure_init);
 /**
  * unpoison_memory - Unpoison a previously poisoned page
  * @pfn: Page number of the to be unpoisoned page
+ * @reset_kpte: Reset the PTE entry for kmap
+ * @reason: The callers tells why unpoisoning the page
  *
- * Software-unpoison a page that has been poisoned by
- * memory_failure() earlier.
+ * Unpoison a page that has been poisoned by memory_failure() earlier.
  *
- * This is only done on the software-level, so it only works
- * for linux injected failures, not real hardware failures
+ * For linux injected failures, there is no need to reset PTE entry.
+ * It's possible to fix hardware memory failure on a virtualization platform,
+ * once hypervisor fixes the failure, guest needs put page back to buddy and
+ * reset the PTE entry in kernel.
  *
  * Returns 0 for success, otherwise -errno.
  */
-int unpoison_memory(unsigned long pfn)
+int unpoison_memory(unsigned long pfn, bool reset_kpte, const char *reason)
 {
 	struct page *page;
 	struct page *p;
 	int ret = -EBUSY;
 	int freeit = 0;
+	pte_t *kpte;
+	unsigned long addr;
 	static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
 					DEFAULT_RATELIMIT_BURST);
 
@@ -2208,8 +2213,15 @@ int unpoison_memory(unsigned long pfn)
 	mutex_unlock(&mf_mutex);
 	if (!ret || freeit) {
 		num_poisoned_pages_dec();
-		unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
-				 page_to_pfn(p), &unpoison_rs);
+		pr_info("Unpoison: Unpoisoned page %#lx by %s\n",
+				 page_to_pfn(p), reason);
+		if (reset_kpte) {
+			preempt_disable();
+			addr = (unsigned long)page_to_virt(p);
+			kpte = virt_to_kpte(addr);
+			set_pte_at(&init_mm, addr, kpte, pfn_pte(pfn, PAGE_KERNEL));
+			preempt_enable();
+		}
 	}
 	return ret;
 }
-- 
2.20.1

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