mm: add spurious fault fixing support for huge pmd

The page faults may be spurious because of the racy access to the page
table.  For example, a non-populated virtual page is accessed on 2
CPUs simultaneously, thus the page faults are triggered on both CPUs.
However, it's possible that one CPU (say CPU A) cannot find the reason
for the page fault if the other CPU (say CPU B) has changed the page
table before the PTE is checked on CPU A.  Most of the time, the
spurious page faults can be ignored safely.  However, if the page
fault is for the write access, it's possible that a stale read-only
TLB entry exists in the local CPU and needs to be flushed on some
architectures.  This is called the spurious page fault fixing.

In the current kernel, there is spurious fault fixing support for pte,
but not for huge pmd because no architectures need it. But in the
next patch in the series, we will change the write protection fault
handling logic on arm64, so that some stale huge pmd entries may
remain in the TLB. These entries need to be flushed via the huge pmd
spurious fault fixing mechanism.

Signed-off-by: Huang Ying <ying.huang@linux.alibaba.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Will Deacon <will@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: Christoph Lameter (Ampere) <cl@gentwo.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Yin Fengwei <fengwei_yin@linux.alibaba.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 21 insertions, 12 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1b81680b4225..6a8679907eaa 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1641,17 +1641,30 @@ vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio,
 EXPORT_SYMBOL_GPL(vmf_insert_folio_pud);
 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
 
-void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
+/**
+ * touch_pmd - Mark page table pmd entry as accessed and dirty (for write)
+ * @vma: The VMA covering @addr
+ * @addr: The virtual address
+ * @pmd: pmd pointer into the page table mapping @addr
+ * @write: Whether it's a write access
+ *
+ * Return: whether the pmd entry is changed
+ */
+bool touch_pmd(struct vm_area_struct *vma, unsigned long addr,
 	       pmd_t *pmd, bool write)
 {
-	pmd_t _pmd;
+	pmd_t entry;
 
-	_pmd = pmd_mkyoung(*pmd);
+	entry = pmd_mkyoung(*pmd);
 	if (write)
-		_pmd = pmd_mkdirty(_pmd);
+		entry = pmd_mkdirty(entry);
 	if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
-				  pmd, _pmd, write))
+				  pmd, entry, write)) {
 		update_mmu_cache_pmd(vma, addr, pmd);
+		return true;
+	}
+
+	return false;
 }
 
 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
@@ -1841,18 +1854,14 @@ unlock:
 }
 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
 
-void huge_pmd_set_accessed(struct vm_fault *vmf)
+bool huge_pmd_set_accessed(struct vm_fault *vmf)
 {
 	bool write = vmf->flags & FAULT_FLAG_WRITE;
 
-	vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
 	if (unlikely(!pmd_same(*vmf->pmd, vmf->orig_pmd)))
-		goto unlock;
-
-	touch_pmd(vmf->vma, vmf->address, vmf->pmd, write);
+		return false;
 
-unlock:
-	spin_unlock(vmf->ptl);
+	return touch_pmd(vmf->vma, vmf->address, vmf->pmd, write);
 }
 
 static vm_fault_t do_huge_zero_wp_pmd(struct vm_fault *vmf)