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Date:   Wed, 10 Mar 2021 14:10:42 +0800
From:   Aili Yao <yaoaili@kingsoft.com>
To:     "Luck, Tony" <tony.luck@intel.com>
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Subject: Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned
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On Fri, 5 Mar 2021 15:55:25 +0000
"Luck, Tony" <tony.luck@intel.com> wrote:

> > From the walk, it seems we have got the virtual address, can we just send a SIGBUS with it?  
> 
> If the walk wins the race and the pte for the poisoned page is still valid, then yes.
> 
> But we could have:
> 
> CPU1                            CPU2
> memory_failure sets poison
> bit for struct page
> 
> 
> rmap finds page in task
> on CPU2 and sets PTE
> to not-valid-poison
> 
>                                 memory_failure returns
>                                 early because struct page
>                                 already marked as poison
> 
>                                 walk page tables looking
>                                 for mapping - don't find it
> 
> -Tony

While I don't think there is a race condition, and if you really think the pfn with SIGBUS is not
proper, I think following patch maybe one way.
I copy your abandon code, and make a little modification, and just now it pass
my simple test.

And also this is a RFC version, only valid if you think the pfn with SIGBUS is not right.

Thanks!

From a522ab8856e3a332a2318d57bb19f3c59594d462 Mon Sep 17 00:00:00 2001
From: Aili Yao <yaoaili@kingsoft.com>
Date: Wed, 10 Mar 2021 13:59:18 +0800
Subject: [PATCH] x86/mce: fix invalid SIGBUS address

walk the current process pte and compare with the pfn;
1. only test for normal page and 2M hugetlb page;
2. 1G hugetlb and transparentHuge is not support currently;
3. May other fails is not recognized, This is a RFC version.

---
 arch/x86/kernel/cpu/mce/core.c | 83 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 80 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index db4afc5..65d7ef7 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -28,8 +28,12 @@
 #include <linux/sysfs.h>
 #include <linux/types.h>
 #include <linux/slab.h>
+#include <linux/hugetlb.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
 #include <linux/init.h>
 #include <linux/kmod.h>
+#include <linux/pagewalk.h>
 #include <linux/poll.h>
 #include <linux/nmi.h>
 #include <linux/cpu.h>
@@ -1235,6 +1239,81 @@ static void __mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *fin
 	/* mce_clear_state will clear *final, save locally for use later */
 	*m = *final;
 }
+static int mc_pte_entry(pte_t *pte, unsigned long addr, unsigned long next, struct mm_walk *walk)
+{
+	u64 *buff = (u64 *)walk->private;
+	u64 pfn = buff[0];
+
+	if (!pte_present(*pte) && is_hwpoison_entry(pte_to_swp_entry(*pte)))
+		goto find;
+	else if (pte_pfn(*pte) == pfn)
+		goto find;
+
+	return 0;
+find:
+	buff[0] = addr;
+	buff[1] = PAGE_SHIFT;
+	return true;
+}
+
+extern bool is_hugetlb_entry_hwpoisoned(pte_t pte);
+
+static int mc_hugetlb_range(pte_t *ptep, unsigned long hmask,
+				 unsigned long addr, unsigned long end,
+				 struct mm_walk *walk)
+{
+	u64 *buff = (u64 *)walk->private;
+	u64 pfn = buff[0];
+	int shift = PMD_SHIFT;
+	pte_t pte =  huge_ptep_get(ptep);
+
+	if (unlikely(is_hugetlb_entry_hwpoisoned(pte)))
+		goto find;
+
+	if (pte_pfn(*ptep) == pfn)
+		goto find;
+
+	return 0;
+find:
+	buff[0] = addr;
+	buff[1] = shift;
+	return true;
+}
+
+static struct mm_walk_ops walk = {
+	.pte_entry = mc_pte_entry,
+	.hugetlb_entry	= mc_hugetlb_range
+};
+
+void mc_memory_failure_error(struct task_struct *p, unsigned long pfn)
+{
+	u64 buff[2] = {pfn, 0};
+	struct page *page;
+	int ret = -1;
+
+	page = pfn_to_page(pfn);
+	if (!page)
+		goto force_sigbus;
+
+	if (is_zone_device_page(page))
+		goto force_sigbus;
+
+	mmap_read_lock(p->mm);
+	ret = walk_page_range(p->mm, 0, TASK_SIZE_MAX, &walk, (void *)buff);
+	mmap_read_unlock(p->mm);
+
+	if (ret && buff[0]) {
+		pr_err("Memory error may not recovered: %#llx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
+		buff[0], p->comm, p->pid);
+		force_sig_mceerr(BUS_MCEERR_AR, (void __user *)buff[0], buff[1]);
+	} else {
+force_sigbus:
+		pr_err("Memory error may not recovered, pfn: %#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
+		pfn, p->comm, p->pid);
+		force_sig_mceerr(BUS_MCEERR_AR, (void __user *)pfn, PAGE_SHIFT);
+	}
+
+}
 
 static void kill_me_now(struct callback_head *ch)
 {
@@ -1259,9 +1338,7 @@ static void kill_me_maybe(struct callback_head *cb)
 	}
 
 	if (p->mce_vaddr != (void __user *)-1l) {
-		pr_err("Memory error may not recovered: %#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
-			p->mce_addr >> PAGE_SHIFT, p->comm, p->pid);
-		force_sig_mceerr(BUS_MCEERR_AR, p->mce_vaddr, PAGE_SHIFT);
+		mc_memory_failure_error(current, p->mce_addr >> PAGE_SHIFT);
 	} else {
 		pr_err("Memory error not recovered");
 		kill_me_now(cb);
-- 
1.8.3.1


-- 
Thanks!
Aili Yao