Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

Luck, Tony
2021-03-03T11:41:01Z

On Fri, Feb 26, 2021 at 10:59:15AM +0800, Aili Yao wrote:
> Hi naoya, tony:
> > >
> > > Idea for what we should do next ... Now that x86 is calling memory_failure()
> > > from user context ... maybe parallel calls for the same page should
> > > be blocked until the first caller completes so we can:
> > > a) know that pages are unmapped (if that happens)
> > > b) all get the same success/fail status
> >
> > One memory_failure() call changes the target page's status and
> > affects all mappings to all affected processes, so I think that
> > (ideally) we don't have to block other threads (letting them
> > early return seems fine). Sometimes memory_failure() fails,
> > but even in such case, PG_hwpoison is set on the page and other
> > threads properly get SIGBUSs with this patch, so I think that
> > we can avoid the worst scenario (like system stall by MCE loop).
> >
> I agree with naoya's point, if we block for this issue, Does this change the result
> that the process should be killed? Or is there something other still need to be considered?

Ok ... no blocking ... I think someone in this thread suggested
scanning the page tables to make sure the poisoned page had been
unmapped.

There's a walk_page_range() function that does all the work for that.
Just need to supply some callback routines that check whether a
mapping includes the bad PFN and clear the PRESENT bit.

RFC patch below against v5.12-rc1

-Tony

From 8de23b7f1be00ad38e129690dfe0b1558fad5ff8 Mon Sep 17 00:00:00 2001
From: Tony Luck <tony.luck@intel.com>
Date: Tue, 2 Mar 2021 15:06:33 -0800
Subject: [PATCH] x86/mce: Handle races between machine checks

When multiple CPUs hit the same poison memory there is a race. The
first CPU into memory_failure() atomically marks the page as poison
and continues processing to hunt down all the tasks that map this page
so that the virtual addresses can be marked not-present and SIGBUS
sent to the task that did the access.

Later CPUs get an early return from memory_failure() and may return
to user mode and access the poison again.

Add a new argument to memory_failure() so that it can indicate when
the race has been lost. Fix kill_me_maybe() to scan page tables in
this case to unmap pages.
---
arch/x86/kernel/cpu/mce/core.c | 61 +++++++++++++++++++++++++++++++---
drivers/base/memory.c | 2 +-
include/linux/mm.h | 2 +-
mm/hwpoison-inject.c | 2 +-
mm/madvise.c | 2 +-
mm/memory-failure.c | 6 ++--
6 files changed, 64 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 7962355436da..2c6c560f3f92 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -30,6 +30,7 @@
#include <linux/slab.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>
@@ -637,6 +638,7 @@ static int uc_decode_notifier(struct notifier_block *nb, unsigned long val,
{
struct mce *mce = (struct mce *)data;
unsigned long pfn;
+ int already = 0;

if (!mce || !mce_usable_address(mce))
return NOTIFY_DONE;
@@ -646,8 +648,9 @@ static int uc_decode_notifier(struct notifier_block *nb, unsigned long val,
return NOTIFY_DONE;

pfn = mce->addr >> PAGE_SHIFT;
- if (!memory_failure(pfn, 0)) {
- set_mce_nospec(pfn, whole_page(mce));
+ if (!memory_failure(pfn, 0, &already)) {
+ if (!already)
+ set_mce_nospec(pfn, whole_page(mce));
mce->kflags |= MCE_HANDLED_UC;
}

@@ -1248,6 +1251,50 @@ static void __mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *fin
*m = *final;
}

+static int pte_entry(pte_t *pte, unsigned long addr, unsigned long next, struct mm_walk *walk)
+{
+ u64 pfn = (u64)walk->private;
+
+ if (pte_pfn(*pte) == pfn)
+ pte->pte = pte->pte & ~_PAGE_PRESENT;
+
+ return 0;
+}
+
+static int pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next, struct mm_walk *walk)
+{
+ int shift = PMD_SHIFT - PAGE_SHIFT;
+ u64 pfn = (u64)walk->private;
+
+ if (!pmd_large(*pmd))
+ return 0;
+
+ if (pmd_pfn(*pmd) >> shift == pfn >> shift)
+ pmd->pmd = pmd->pmd & ~_PAGE_PRESENT;
+
+ return 0;
+}
+
+static int pud_entry(pud_t *pud, unsigned long addr, unsigned long next, struct mm_walk *walk)
+{
+ int shift = PUD_SHIFT - PAGE_SHIFT;
+ u64 pfn = (u64)walk->private;
+
+ if (!pud_large(*pud))
+ return 0;
+
+ if (pud_pfn(*pud) >> shift == pfn >> shift)
+ pud->pud = pud->pud & ~_PAGE_PRESENT;
+
+ return 0;
+}
+
+static struct mm_walk_ops walk = {
+ .pte_entry = pte_entry,
+ .pmd_entry = pmd_entry,
+ .pud_entry = pud_entry
+};
+
static void kill_me_now(struct callback_head *ch)
{
force_sig(SIGBUS);
@@ -1257,15 +1304,19 @@ static void kill_me_maybe(struct callback_head *cb)
{
struct task_struct *p = container_of(cb, struct task_struct, mce_kill_me);
int flags = MF_ACTION_REQUIRED;
+ int already = 0;

pr_err("Uncorrected hardware memory error in user-access at %llx", p->mce_addr);

if (!p->mce_ripv)
flags |= MF_MUST_KILL;

- if (!memory_failure(p->mce_addr >> PAGE_SHIFT, flags) &&
+ if (!memory_failure(p->mce_addr >> PAGE_SHIFT, flags, &already) &&
!(p->mce_kflags & MCE_IN_KERNEL_COPYIN)) {
- set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
+ if (already)
+ walk_page_range(current->mm, 0, TASK_SIZE_MAX, &walk, (void *)(p->mce_addr >> PAGE_SHIFT));
+ else
+ set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
sync_core();
return;
}
@@ -1452,7 +1503,7 @@ noinstr void do_machine_check(struct pt_regs *regs)
EXPORT_SYMBOL_GPL(do_machine_check);

#ifndef CONFIG_MEMORY_FAILURE
-int memory_failure(unsigned long pfn, int flags)
+int memory_failure(unsigned long pfn, int flags, int *already)
{
/* mce_severity() should not hand us an ACTION_REQUIRED error */
BUG_ON(flags & MF_ACTION_REQUIRED);
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index f35298425575..144500983656 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -480,7 +480,7 @@ static ssize_t hard_offline_page_store(struct device *dev,
if (kstrtoull(buf, 0, &pfn) < 0)
return -EINVAL;
pfn >>= PAGE_SHIFT;
- ret = memory_failure(pfn, 0);
+ ret = memory_failure(pfn, 0, NULL);
return ret ? ret : count;
}

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 77e64e3eac80..beaa6e871cbe 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3003,7 +3003,7 @@ enum mf_flags {
MF_MUST_KILL = 1 << 2,
MF_SOFT_OFFLINE = 1 << 3,
};
-extern int memory_failure(unsigned long pfn, int flags);
+extern int memory_failure(unsigned long pfn, int flags, int *already);
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);
diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
index 1ae1ebc2b9b1..bfd5151dcd3f 100644
--- a/mm/hwpoison-inject.c
+++ b/mm/hwpoison-inject.c
@@ -48,7 +48,7 @@ static int hwpoison_inject(void *data, u64 val)

inject:
pr_info("Injecting memory failure at pfn %#lx\n", pfn);
- return memory_failure(pfn, 0);
+ return memory_failure(pfn, 0, NULL);
}

static int hwpoison_unpoison(void *data, u64 val)
diff --git a/mm/madvise.c b/mm/madvise.c
index df692d2e35d4..09f569fed68d 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -908,7 +908,7 @@ static int madvise_inject_error(int behavior,
} else {
pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
pfn, start);
- ret = memory_failure(pfn, MF_COUNT_INCREASED);
+ ret = memory_failure(pfn, MF_COUNT_INCREASED, NULL);
}

if (ret)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 24210c9bd843..9a8911aa5fc9 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1398,7 +1398,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
* Must run in process context (e.g. a work queue) with interrupts
* enabled and no spinlocks hold.
*/
-int memory_failure(unsigned long pfn, int flags)
+int memory_failure(unsigned long pfn, int flags, int *already)
{
struct page *p;
struct page *hpage;
@@ -1428,6 +1428,8 @@ int memory_failure(unsigned long pfn, int flags)
if (PageHuge(p))
return memory_failure_hugetlb(pfn, flags);
if (TestSetPageHWPoison(p)) {
+ if (already)
+ *already = 1;
pr_err("Memory failure: %#lx: already hardware poisoned\n",
pfn);
return 0;
@@ -1634,7 +1636,7 @@ static void memory_failure_work_func(struct work_struct *work)
if (entry.flags & MF_SOFT_OFFLINE)
soft_offline_page(entry.pfn, entry.flags);
else
- memory_failure(entry.pfn, entry.flags);
+ memory_failure(entry.pfn, entry.flags, NULL);
}
}

--
2.29.2