mce: fix set_mce_nospec to always unmap the whole page

The set_memory_uc() approach doesn't work well in all cases.
As Dan pointed out 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,
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/[e-mail]/

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

Fixes: 284ce4011ba6 ("x86/memory_failure: Introduce {set, clear}_mce_nospec()")
Reviewed-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Dan Williams <[e-mail]>
Signed-off-by: Jane Chu <[e-mail]>
Acked-by: Tony Luck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dan Williams <[e-mail]>

arch/x86/kernel/cpu/mce/core.c

···
 
 	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;
 	}
 
···
 
 	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;
 	}
···
 	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 *))

arch/x86/mm/pat/set_memory.c

···
 }
 EXPORT_SYMBOL(set_memory_wb);
 
-/*
- * 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).
- */
+/* Prevent speculative access to a page by marking it not-present */
 #ifdef CONFIG_X86_64
-int set_mce_nospec(unsigned long pfn, bool unmap)
+int set_mce_nospec(unsigned long pfn)
 {
 	unsigned long decoy_addr;
 	int rc;
···
 	 */
 	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;
 }
 
+static int set_memory_present(unsigned long *addr, int numpages)
+{
+	return change_page_attr_set(addr, numpages, __pgprot(_PAGE_PRESENT), 0);
+}
+
 /* 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 set_memory_present(&addr, 1);
 }
 EXPORT_SYMBOL_GPL(clear_mce_nospec);
 #endif /* CONFIG_X86_64 */

drivers/nvdimm/pmem.c

···
 			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.
-	 */
-	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);
+		if (rc != BLK_STS_OK)
+			return rc;
 	}
 
-	return rc;
+	flush_dcache_page(page);
+	write_pmem(pmem_addr, page, page_off, len);
+
+	return BLK_STS_OK;
 }
 
 static void pmem_submit_bio(struct bio *bio)

include/linux/set_memory.h

···
 #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;
 }