[PATCH v14 10/26] x86/mm: Update pte_modify for _PAGE_COW

[Yu-cheng Yu]

Pte_modify() changes a PTE to 'newprot'.  It doesn't use the pte_*()
helpers that a previous patch fixed up, so we need a new site.

Introduce fixup_dirty_pte() to set the dirty bits based on _PAGE_RW, and
apply the same changes to pmd_modify().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>

v14:
- Update fixup_dirty_pte() and fixup_dirty_pmd() with
  cpu_feature_enabled(X86_FEATURE_SHSTK).

v10:
- Replace _PAGE_CHG_MASK approach with fixup functions.
---
 arch/x86/include/asm/pgtable.h | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index ac4ed814be96..8d4c09831e67 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -727,6 +727,21 @@ static inline pmd_t pmd_mkinvalid(pmd_t pmd)
 
 static inline u64 flip_protnone_guard(u64 oldval, u64 val, u64 mask);
 
+static inline pteval_t fixup_dirty_pte(pteval_t pteval)
+{
+	pte_t pte = __pte(pteval);
+
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK) && pte_dirty(pte)) {
+		pte = pte_mkclean(pte);
+
+		if (pte_flags(pte) & _PAGE_RW)
+			pte = pte_set_flags(pte, _PAGE_DIRTY_HW);
+		else
+			pte = pte_set_flags(pte, _PAGE_COW);
+	}
+	return pte_val(pte);
+}
+
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
 	pteval_t val = pte_val(pte), oldval = val;
@@ -737,16 +752,34 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 	 */
 	val &= _PAGE_CHG_MASK;
 	val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK;
+	val = fixup_dirty_pte(val);
 	val = flip_protnone_guard(oldval, val, PTE_PFN_MASK);
 	return __pte(val);
 }
 
+static inline int pmd_write(pmd_t pmd);
+static inline pmdval_t fixup_dirty_pmd(pmdval_t pmdval)
+{
+	pmd_t pmd = __pmd(pmdval);
+
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK) && pmd_dirty(pmd)) {
+		pmd = pmd_mkclean(pmd);
+
+		if (pmd_flags(pmd) & _PAGE_RW)
+			pmd = pmd_set_flags(pmd, _PAGE_DIRTY_HW);
+		else
+			pmd = pmd_set_flags(pmd, _PAGE_COW);
+	}
+	return pmd_val(pmd);
+}
+
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 {
 	pmdval_t val = pmd_val(pmd), oldval = val;
 
 	val &= _HPAGE_CHG_MASK;
 	val |= check_pgprot(newprot) & ~_HPAGE_CHG_MASK;
+	val = fixup_dirty_pmd(val);
 	val = flip_protnone_guard(oldval, val, PHYSICAL_PMD_PAGE_MASK);
 	return __pmd(val);
 }
-- 
2.21.0