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From:   Jane Chu <jane.chu@oracle.com>
To:     david@fromorbit.com, djwong@kernel.org, dan.j.williams@intel.com,
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        linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev,
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        x86@kernel.org
Subject: [PATCH v7 3/6] mce: fix set_mce_nospec to always unmap the whole page
Date:   Tue,  5 Apr 2022 13:47:44 -0600
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The set_memory_uc() approach doesn't work well in all cases.
For example, when "The VMM unmapped the bad page from guest
physical space and passed the machine check to the guest."
"The guest gets virtual #MC on an access to that page.
 When the guest tries to do set_memory_uc() and instructs
 cpa_flush() to do clean caches that results in taking another
 fault / exception perhaps because the VMM unmapped the page
 from the guest."

Since the driver has special knowledge to handle NP or UC,
let's mark the poisoned page with NP and let driver handle it
when it comes down to repair.

Please refer to discussions here for more details.
https://lore.kernel.org/all/CAPcyv4hrXPb1tASBZUg-GgdVs0OOFKXMXLiHmktg_kFi7YBMyQ@mail.gmail.com/

Now since poisoned page is marked as not-present, in order to
avoid writing to a 'np' page and trigger kernel Oops, also fix
pmem_do_write().

Fixes: 284ce4011ba6 ("x86/memory_failure: Introduce {set, clear}_mce_nospec()")
Signed-off-by: Jane Chu <jane.chu@oracle.com>
---
 arch/x86/kernel/cpu/mce/core.c |  6 +++---
 arch/x86/mm/pat/set_memory.c   | 18 ++++++------------
 drivers/nvdimm/pmem.c          | 31 +++++++------------------------
 include/linux/set_memory.h     |  4 ++--
 4 files changed, 18 insertions(+), 41 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 981496e6bc0e..fa67bb9d1afe 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -579,7 +579,7 @@ static int uc_decode_notifier(struct notifier_block *nb, unsigned long val,
 
 	pfn = mce->addr >> PAGE_SHIFT;
 	if (!memory_failure(pfn, 0)) {
-		set_mce_nospec(pfn, whole_page(mce));
+		set_mce_nospec(pfn);
 		mce->kflags |= MCE_HANDLED_UC;
 	}
 
@@ -1316,7 +1316,7 @@ static void kill_me_maybe(struct callback_head *cb)
 
 	ret = memory_failure(p->mce_addr >> PAGE_SHIFT, flags);
 	if (!ret) {
-		set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
+		set_mce_nospec(p->mce_addr >> PAGE_SHIFT);
 		sync_core();
 		return;
 	}
@@ -1342,7 +1342,7 @@ static void kill_me_never(struct callback_head *cb)
 	p->mce_count = 0;
 	pr_err("Kernel accessed poison in user space at %llx\n", p->mce_addr);
 	if (!memory_failure(p->mce_addr >> PAGE_SHIFT, 0))
-		set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
+		set_mce_nospec(p->mce_addr >> PAGE_SHIFT);
 }
 
 static void queue_task_work(struct mce *m, char *msg, void (*func)(struct callback_head *))
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 93dde949f224..404ffcb3f2cb 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1926,13 +1926,8 @@ int set_memory_wb(unsigned long addr, int numpages)
 EXPORT_SYMBOL(set_memory_wb);
 
 #ifdef CONFIG_X86_64
-/*
- * Prevent speculative access to the page by either unmapping
- * it (if we do not require access to any part of the page) or
- * marking it uncacheable (if we want to try to retrieve data
- * from non-poisoned lines in the page).
- */
-int set_mce_nospec(unsigned long pfn, bool unmap)
+/* Prevent speculative access to a page by marking it not-present */
+int set_mce_nospec(unsigned long pfn)
 {
 	unsigned long decoy_addr;
 	int rc;
@@ -1954,10 +1949,7 @@ int set_mce_nospec(unsigned long pfn, bool unmap)
 	 */
 	decoy_addr = (pfn << PAGE_SHIFT) + (PAGE_OFFSET ^ BIT(63));
 
-	if (unmap)
-		rc = set_memory_np(decoy_addr, 1);
-	else
-		rc = set_memory_uc(decoy_addr, 1);
+	rc = set_memory_np(decoy_addr, 1);
 	if (rc)
 		pr_warn("Could not invalidate pfn=0x%lx from 1:1 map\n", pfn);
 	return rc;
@@ -1966,7 +1958,9 @@ int set_mce_nospec(unsigned long pfn, bool unmap)
 /* Restore full speculative operation to the pfn. */
 int clear_mce_nospec(unsigned long pfn)
 {
-	return set_memory_wb((unsigned long) pfn_to_kaddr(pfn), 1);
+	unsigned long addr = (unsigned long) pfn_to_kaddr(pfn);
+
+	return change_page_attr_set(&addr, 1, __pgprot(_PAGE_PRESENT), 0);
 }
 EXPORT_SYMBOL_GPL(clear_mce_nospec);
 
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 58d95242a836..30c71a68175b 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -158,36 +158,19 @@ static blk_status_t pmem_do_write(struct pmem_device *pmem,
 			struct page *page, unsigned int page_off,
 			sector_t sector, unsigned int len)
 {
-	blk_status_t rc = BLK_STS_OK;
-	bool bad_pmem = false;
 	phys_addr_t pmem_off = sector * 512 + pmem->data_offset;
 	void *pmem_addr = pmem->virt_addr + pmem_off;
 
-	if (unlikely(is_bad_pmem(&pmem->bb, sector, len)))
-		bad_pmem = true;
+	if (unlikely(is_bad_pmem(&pmem->bb, sector, len))) {
+		blk_status_t rc = pmem_clear_poison(pmem, pmem_off, len);
 
-	/*
-	 * Note that we write the data both before and after
-	 * clearing poison.  The write before clear poison
-	 * handles situations where the latest written data is
-	 * preserved and the clear poison operation simply marks
-	 * the address range as valid without changing the data.
-	 * In this case application software can assume that an
-	 * interrupted write will either return the new good
-	 * data or an error.
-	 *
-	 * However, if pmem_clear_poison() leaves the data in an
-	 * indeterminate state we need to perform the write
-	 * after clear poison.
-	 */
+		if (rc != BLK_STS_OK)
+			pr_warn_ratelimited("%s: failed to clear poison\n", __func__);
+			return rc;
+	}
 	flush_dcache_page(page);
 	write_pmem(pmem_addr, page, page_off, len);
-	if (unlikely(bad_pmem)) {
-		rc = pmem_clear_poison(pmem, pmem_off, len);
-		write_pmem(pmem_addr, page, page_off, len);
-	}
-
-	return rc;
+	return BLK_STS_OK;
 }
 
 static void pmem_submit_bio(struct bio *bio)
diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h
index d6263d7afb55..cde2d8687a7b 100644
--- a/include/linux/set_memory.h
+++ b/include/linux/set_memory.h
@@ -43,10 +43,10 @@ static inline bool can_set_direct_map(void)
 #endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */
 
 #ifdef CONFIG_X86_64
-int set_mce_nospec(unsigned long pfn, bool unmap);
+int set_mce_nospec(unsigned long pfn);
 int clear_mce_nospec(unsigned long pfn);
 #else
-static inline int set_mce_nospec(unsigned long pfn, bool unmap)
+static inline int set_mce_nospec(unsigned long pfn)
 {
 	return 0;
 }
-- 
2.18.4