[RFCv2 15/16] KVM: Unmap protected pages from direct mapping

[Kirill A. Shutemov]

If the protected memory feature enabled, unmap guest memory from
kernel's direct mappings.

Migration and KSM is disabled for protected memory as it would require a
special treatment.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 include/linux/mm.h       |  3 +++
 mm/huge_memory.c         |  8 ++++++++
 mm/ksm.c                 |  2 ++
 mm/memory.c              | 12 ++++++++++++
 mm/rmap.c                |  4 ++++
 virt/lib/mem_protected.c | 21 +++++++++++++++++++++
 6 files changed, 50 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ee274d27e764..74efc51e63f0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -671,6 +671,9 @@ static inline bool vma_is_kvm_protected(struct vm_area_struct *vma)
 	return vma->vm_flags & VM_KVM_PROTECTED;
 }
 
+void kvm_map_page(struct page *page, int nr_pages);
+void kvm_unmap_page(struct page *page, int nr_pages);
+
 #ifdef CONFIG_SHMEM
 /*
  * The vma_is_shmem is not inline because it is used only by slow
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ec8cf9a40cfd..40974656cb43 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -627,6 +627,10 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
 		spin_unlock(vmf->ptl);
 		count_vm_event(THP_FAULT_ALLOC);
 		count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
+
+		/* Unmap page from direct mapping */
+		if (vma_is_kvm_protected(vma))
+			kvm_unmap_page(page, HPAGE_PMD_NR);
 	}
 
 	return 0;
@@ -1689,6 +1693,10 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 			page_remove_rmap(page, true);
 			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
 			VM_BUG_ON_PAGE(!PageHead(page), page);
+
+			/* Map the page back to the direct mapping */
+			if (vma_is_kvm_protected(vma))
+				kvm_map_page(page, HPAGE_PMD_NR);
 		} else if (thp_migration_supported()) {
 			swp_entry_t entry;
 
diff --git a/mm/ksm.c b/mm/ksm.c
index 9afccc36dbd2..c720e271448f 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -528,6 +528,8 @@ static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
 		return NULL;
 	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 		return NULL;
+	if (vma_is_kvm_protected(vma))
+		return NULL;
 	return vma;
 }
 
diff --git a/mm/memory.c b/mm/memory.c
index 2c9756b4e52f..e28bd5f902a7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1245,6 +1245,11 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 				    likely(!(vma->vm_flags & VM_SEQ_READ)))
 					mark_page_accessed(page);
 			}
+
+			/* Map the page back to the direct mapping */
+			if (vma_is_anonymous(vma) && vma_is_kvm_protected(vma))
+				kvm_map_page(page, 1);
+
 			rss[mm_counter(page)]--;
 			page_remove_rmap(page, false);
 			if (unlikely(page_mapcount(page) < 0))
@@ -3466,6 +3471,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 	struct page *page;
 	vm_fault_t ret = 0;
 	pte_t entry;
+	bool set = false;
 
 	/* File mapping without ->vm_ops ? */
 	if (vma->vm_flags & VM_SHARED)
@@ -3554,6 +3560,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
 	page_add_new_anon_rmap(page, vma, vmf->address, false);
 	lru_cache_add_inactive_or_unevictable(page, vma);
+	set = true;
 setpte:
 	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry);
 
@@ -3561,6 +3568,11 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 	update_mmu_cache(vma, vmf->address, vmf->pte);
 unlock:
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
+
+	/* Unmap page from direct mapping */
+	if (vma_is_kvm_protected(vma) && set)
+		kvm_unmap_page(page, 1);
+
 	return ret;
 release:
 	put_page(page);
diff --git a/mm/rmap.c b/mm/rmap.c
index 9425260774a1..247548d6d24b 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1725,6 +1725,10 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 
 static bool invalid_migration_vma(struct vm_area_struct *vma, void *arg)
 {
+	/* TODO */
+	if (vma_is_kvm_protected(vma))
+		return true;
+
 	return vma_is_temporary_stack(vma);
 }
 
diff --git a/virt/lib/mem_protected.c b/virt/lib/mem_protected.c
index 1dfe82534242..9d2ef99285e5 100644
--- a/virt/lib/mem_protected.c
+++ b/virt/lib/mem_protected.c
@@ -30,6 +30,27 @@ void kvm_unmap_page_atomic(void *vaddr)
 }
 EXPORT_SYMBOL_GPL(kvm_unmap_page_atomic);
 
+void kvm_map_page(struct page *page, int nr_pages)
+{
+	int i;
+
+	/* Clear page before returning it to the direct mapping */
+	for (i = 0; i < nr_pages; i++) {
+		void *p = kvm_map_page_atomic(page + i);
+		memset(p, 0, PAGE_SIZE);
+		kvm_unmap_page_atomic(p);
+	}
+
+	kernel_map_pages(page, nr_pages, 1);
+}
+EXPORT_SYMBOL_GPL(kvm_map_page);
+
+void kvm_unmap_page(struct page *page, int nr_pages)
+{
+	kernel_map_pages(page, nr_pages, 0);
+}
+EXPORT_SYMBOL_GPL(kvm_unmap_page);
+
 int kvm_init_protected_memory(void)
 {
 	guest_map_ptes = kmalloc_array(num_possible_cpus(),
-- 
2.26.2