[RFC PATCH v9 15/27] mm: Handle THP/HugeTLB Shadow Stack page fault

[Yu-cheng Yu]

This patch implements THP Shadow Stack (SHSTK) copying in the same way as
in the previous patch for regular PTE.

In copy_huge_pmd(), clear the dirty bit from the PMD to cause a page fault
upon the next SHSTK access to the PMD.  At that time, fix the PMD and
copy/re-use the page.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
 arch/x86/mm/pgtable.c         |  8 ++++++++
 include/asm-generic/pgtable.h | 11 +++++++++++
 mm/huge_memory.c              |  4 ++++
 3 files changed, 23 insertions(+)

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 2eb33794c08d..3340b1d4e9da 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -886,4 +886,12 @@ inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma)
 	else
 		return pte;
 }
+
+inline pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma)
+{
+	if (vma->vm_flags & VM_SHSTK)
+		return pmd_mkdirty_shstk(pmd);
+	else
+		return pmd;
+}
 #endif /* CONFIG_X86_INTEL_SHADOW_STACK_USER */
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 9cb2f9ba5895..a9df093fdf45 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -1201,9 +1201,20 @@ static inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma)
 {
 	return pte;
 }
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma)
+{
+	return pmd;
+}
+#endif
 #else
 bool arch_copy_pte_mapping(vm_flags_t vm_flags);
 pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma);
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma);
+#endif
 #endif
 #endif /* CONFIG_MMU */
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a88093213674..93ef368df2dd 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -636,6 +636,7 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
 
 		entry = mk_huge_pmd(page, vma->vm_page_prot);
 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+		entry = pmd_set_vma_features(entry, vma);
 		page_add_new_anon_rmap(page, vma, haddr, true);
 		mem_cgroup_commit_charge(page, memcg, false, true);
 		lru_cache_add_active_or_unevictable(page, vma);
@@ -1278,6 +1279,7 @@ static vm_fault_t do_huge_pmd_wp_page_fallback(struct vm_fault *vmf,
 		pte_t entry;
 		entry = mk_pte(pages[i], vma->vm_page_prot);
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		entry = pte_set_vma_features(entry, vma);
 		memcg = (void *)page_private(pages[i]);
 		set_page_private(pages[i], 0);
 		page_add_new_anon_rmap(pages[i], vmf->vma, haddr, false);
@@ -1360,6 +1362,7 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
 		pmd_t entry;
 		entry = pmd_mkyoung(orig_pmd);
 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+		entry = pmd_set_vma_features(entry, vma);
 		if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry,  1))
 			update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
 		ret |= VM_FAULT_WRITE;
@@ -1432,6 +1435,7 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
 		pmd_t entry;
 		entry = mk_huge_pmd(new_page, vma->vm_page_prot);
 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+		entry = pmd_set_vma_features(entry, vma);
 		pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
 		page_add_new_anon_rmap(new_page, vma, haddr, true);
 		mem_cgroup_commit_charge(new_page, memcg, false, true);
-- 
2.21.0