LoongArch: Let {pte,pmd}_modify() record the status of _PAGE_DIRTY

Now if the PTE/PMD is dirty with _PAGE_DIRTY but without _PAGE_MODIFIED,
after {pte,pmd}_modify() we lose _PAGE_DIRTY, then {pte,pmd}_dirty()
return false and lead to data loss. This can happen in certain scenarios
such as HW PTW doesn't set _PAGE_MODIFIED automatically, so here we need
_PAGE_MODIFIED to record the dirty status (_PAGE_DIRTY).

The new modification involves checking whether the original PTE/PMD has
the _PAGE_DIRTY flag. If it exists, the _PAGE_MODIFIED bit is also set,
ensuring that the {pte,pmd}_dirty() interface can always return accurate
information.

Cc: stable@vger.kernel.org
Co-developed-by: Liupu Wang <wangliupu@loongson.cn>
Signed-off-by: Liupu Wang <wangliupu@loongson.cn>
Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>

Author: zhangtianyang-zty

arch/loongarch/include/asm/pgtable.h

@@ -424,6 +424,9 @@ static inline unsigned long pte_accessible(struct mm_struct *mm, pte_t a)
 
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
+	if (pte_val(pte) & _PAGE_DIRTY)
+		pte_val(pte) |= _PAGE_MODIFIED;
+
 	return __pte((pte_val(pte) & _PAGE_CHG_MASK) |
 		     (pgprot_val(newprot) & ~_PAGE_CHG_MASK));
 }
@@ -547,9 +550,11 @@ static inline struct page *pmd_page(pmd_t pmd)
 
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 {
-	pmd_val(pmd) = (pmd_val(pmd) & _HPAGE_CHG_MASK) |
-				(pgprot_val(newprot) & ~_HPAGE_CHG_MASK);
-	return pmd;
+	if (pmd_val(pmd) & _PAGE_DIRTY)
+		pmd_val(pmd) |= _PAGE_MODIFIED;
+
+	return __pmd((pmd_val(pmd) & _HPAGE_CHG_MASK) |
+		     (pgprot_val(newprot) & ~_HPAGE_CHG_MASK));
 }
 
 static inline pmd_t pmd_mkinvalid(pmd_t pmd)