Subject: [PATCH v4 2/5] live migration support for initial write protect of VM

From: [email-masked] (Mario Smarduch)
Date: Mon, 28 Apr 2014 17:54:56 -0700

Patch adds support for live migration initial split up of huge pages
in memory slot and write protection of all pages in memory slot.

Signed-off-by: Mario Smarduch <[email-masked]>
---
 arch/arm/include/asm/kvm_host.h |    8 ++
 arch/arm/include/asm/kvm_mmu.h  |   11 ++
 arch/arm/kvm/arm.c              |    3 +
 arch/arm/kvm/mmu.c              |  215 +++++++++++++++++++++++++++++++++++++++
 virt/kvm/kvm_main.c             |    5 +-
 5 files changed, 241 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 1e739f9..9f827c8 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -67,6 +67,12 @@ struct kvm_arch {
 
 	/* Interrupt controller */
 	struct vgic_dist	vgic;
+
+	/* Marks start of migration, used to handle 2nd stage page faults
+	 * during migration, prevent installing huge pages and split huge pages
+	 * to small pages.
+	 */
+	int migration_in_progress;
 };
 
 #define KVM_NR_MEM_OBJS     40
@@ -230,4 +236,6 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *, u64 regid, u64 value);
 
 void kvm_tlb_flush_vmid(struct kvm *kvm);
 
+int kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
+
 #endif /* __ARM_KVM_HOST_H__ */
diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index a91c863..342ae81 100644
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -111,6 +111,17 @@ static inline void kvm_set_s2pte_writable(pte_t *pte)
 	pte_val(*pte) |= L_PTE_S2_RDWR;
 }
 
+static inline void kvm_set_s2pte_readonly(pte_t *pte)
+{
+	pte_val(*pte) &= ~(L_PTE_S2_RDONLY ^ L_PTE_S2_RDWR);
+}
+
+static inline bool kvm_s2pte_readonly(pte_t *pte)
+{
+	return (pte_val(*pte) & L_PTE_S2_RDWR) == L_PTE_S2_RDONLY;
+}
+
+
 static inline void kvm_set_s2pmd_writable(pmd_t *pmd)
 {
 	pmd_val(*pmd) |= L_PMD_S2_RDWR;
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 9a4bc10..b916478 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -233,6 +233,9 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				   struct kvm_userspace_memory_region *mem,
 				   enum kvm_mr_change change)
 {
+	/* Request for migration issued by user, write protect memory slot */
+	if ((change != KVM_MR_DELETE) && (mem->flags & KVM_MEM_LOG_DIRTY_PAGES))
+		return kvm_mmu_slot_remove_write_access(kvm, mem->slot);
 	return 0;
 }
 
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 7ab77f3..15bbca2 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -44,6 +44,41 @@ static phys_addr_t hyp_idmap_vector;
 
 #define kvm_pmd_huge(_x)	(pmd_huge(_x) || pmd_trans_huge(_x))
 
+/* Used for 2nd stage and identity mappings. For stage 2 mappings
+ * instead of unsigned long, u64 is use  which won't overflow on ARMv7 for
+ * IPAs above 4GB. For ARMv8 use default functions.
+ */
+
+static phys_addr_t kvm_pgd_addr_end(phys_addr_t addr, phys_addr_t end)
+{
+#if BITS_PER_LONG == 32
+	u64 __boundary = ((addr) + PGDIR_SIZE) & PGDIR_MASK;
+	return __boundary - 1 < end - 1 ? __boundary : end;
+#else
+	return pgd_addr_end(addr, end);
+#endif
+}
+
+static phys_addr_t kvm_pud_addr_end(phys_addr_t addr, phys_addr_t end)
+{
+#if BITS_PER_LONG == 32
+	u64 __boundary = ((addr) + PUD_SIZE) & PUD_MASK;
+	return __boundary - 1 < end - 1 ? __boundary : end;
+#else
+	return pud_addr_end(addr, end);
+#endif
+}
+
+static phys_addr_t kvm_pmd_addr_end(phys_addr_t addr, phys_addr_t end)
+{
+#if BITS_PER_LONG == 32
+	u64 __boundary = ((addr) + PMD_SIZE) & PMD_MASK;
+	return __boundary - 1 < end - 1 ? __boundary : end;
+#else
+	return pmd_addr_end(addr, end);
+#endif
+}
+
 static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
 {
 	/*
@@ -649,6 +684,186 @@ static bool transparent_hugepage_adjust(pfn_t *pfnp, phys_addr_t *ipap)
 	return false;
 }
 
+/**
+ * kvm_split_pmd - splits huge pages to small pages, required to keep a dirty
+ *	log of smaller memory granules, otherwise huge pages would need to be
+ *	migrated. Practically an idle system has problems migrating with
+ *	huge pages.  Called during WP of entire VM address space, done
+ *	initially when  migration thread isses the KVM_MEM_LOG_DIRTY_PAGES
+ *	ioctl.
+ *	The mmu_lock is held during splitting.
+ *
+ * @kvm:        The KVM pointer
+ * @pmd:        Pmd to 2nd stage huge page
+ * @addr:       Guest Physical Address
+ */
+static int kvm_split_pmd(struct kvm *kvm, pmd_t *pmd, u64 addr)
+{
+	struct page *page;
+	pfn_t pfn = pmd_pfn(*pmd);
+	pte_t *pte;
+	int i;
+
+	page = alloc_page(GFP_KERNEL);
+	if (page == NULL)
+		return -ENOMEM;
+
+	pte = page_address(page);
+	/* cycle through ptes first, use pmd pfn */
+	for (i = 0; i < PTRS_PER_PMD; i++)
+		pte[i] = pfn_pte(pfn+i, PAGE_S2);
+
+	kvm_clean_pte(pte);
+	/* After page table setup set pmd */
+	pmd_populate_kernel(NULL, pmd, pte);
+
+	/* get reference on pte page */
+	get_page(virt_to_page(pte));
+	return 0;
+}
+
+/* Walks PMD page table range and write protects it. Called with
+ * 'kvm->mmu_lock'  held
+ */
+static void stage2_wp_pmd_range(phys_addr_t addr, phys_addr_t end, pmd_t *pmd)
+{
+	pte_t *pte;
+
+	while (addr < end) {
+		pte = pte_offset_kernel(pmd, addr);
+		addr += PAGE_SIZE;
+		if (!pte_present(*pte))
+			continue;
+		/* skip write protected pages */
+		if (kvm_s2pte_readonly(pte))
+			continue;
+		kvm_set_s2pte_readonly(pte);
+	}
+}
+
+/* Walks PUD  page table range to write protects it , if necessary splits up
+ * huge pages to small pages. Called with 'kvm->mmu_lock' held.
+ */
+static int stage2_wp_pud_range(struct kvm *kvm, phys_addr_t addr,
+				phys_addr_t end, pud_t *pud)
+{
+	pmd_t *pmd;
+	phys_addr_t pmd_end;
+	int ret;
+
+	while (addr < end) {
+		/* If needed give up CPU during PUD page table walk */
+		if (need_resched() || spin_needbreak(&kvm->mmu_lock))
+			cond_resched_lock(&kvm->mmu_lock);
+
+		pmd = pmd_offset(pud, addr);
+		if (!pmd_present(*pmd)) {
+			addr = kvm_pmd_addr_end(addr, end);
+			continue;
+		}
+
+		if (kvm_pmd_huge(*pmd)) {
+			ret = kvm_split_pmd(kvm, pmd, addr);
+			/* Failed to split up huge  page abort. */
+			if (ret < 0)
+				return ret;
+
+			addr = kvm_pmd_addr_end(addr, end);
+			continue;
+		}
+
+		pmd_end = kvm_pmd_addr_end(addr, end);
+		stage2_wp_pmd_range(addr, pmd_end, pmd);
+		addr = pmd_end;
+	}
+	return 0;
+}
+
+/* Walks PGD page table range to write protect it. Called with 'kvm->mmu_lock'
+ * held.
+ */
+static int stage2_wp_pgd_range(struct kvm *kvm, phys_addr_t addr,
+				phys_addr_t end, pgd_t *pgd)
+{
+	phys_addr_t pud_end;
+	pud_t *pud;
+	int ret;
+
+	while (addr < end) {
+		/* give up CPU if mmu_lock is needed by other vCPUs */
+		if (need_resched() || spin_needbreak(&kvm->mmu_lock))
+			cond_resched_lock(&kvm->mmu_lock);
+
+		pud = pud_offset(pgd, addr);
+		if (!pud_present(*pud)) {
+			addr = kvm_pud_addr_end(addr, end);
+			continue;
+		}
+
+		/* Fail if PUD is huge, splitting PUDs not supported */
+		if (pud_huge(*pud))
+			return -EFAULT;
+
+		/* By default 'nopud' is supported which fails with guests
+		 * larger then 1GB. Added to support 4-level page tables.
+		 */
+		pud_end = kvm_pud_addr_end(addr, end);
+		ret = stage2_wp_pud_range(kvm, addr, pud_end, pud);
+		if (ret < 0)
+			return ret;
+		addr = pud_end;
+	}
+	return 0;
+}
+
+/**
+ * kvm_mmu_slot_remove_access - write protects entire memslot address space.
+ *      Called@start of migration when KVM_MEM_LOG_DIRTY_PAGES ioctl is
+ *      issued. After this function returns all pages (minus the ones faulted
+ *      in or released when mmu_lock is give nup) must be write protected to
+ *	keep track of dirty pages to migrate on subsequent dirty log read.
+ *      mmu_lock is held during write protecting, released on contention.
+ *
+ * @kvm:        The KVM pointer
+ * @slot:       The memory slot the dirty log is retrieved for
+ */
+int kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
+{
+	pgd_t *pgd;
+	pgd_t *pgdp = kvm->arch.pgd;
+	struct kvm_memory_slot *memslot = id_to_memslot(kvm->memslots, slot);
+	phys_addr_t addr = memslot->base_gfn << PAGE_SHIFT;
+	phys_addr_t end = (memslot->base_gfn + memslot->npages) << PAGE_SHIFT;
+	phys_addr_t pgdir_end;
+	int ret = -ENOMEM;
+
+	spin_lock(&kvm->mmu_lock);
+	/* set start of migration, sychronize with Data Abort handler */
+	kvm->arch.migration_in_progress = 1;
+
+	/* Walk range, split up huge pages as needed and write protect ptes */
+	while (addr < end) {
+		pgd = pgdp + pgd_index(addr);
+		if (!pgd_present(*pgd)) {
+			addr = kvm_pgd_addr_end(addr, end);
+			continue;
+		}
+
+		pgdir_end = kvm_pgd_addr_end(addr, end);
+		ret = stage2_wp_pgd_range(kvm, addr, pgdir_end, pgd);
+		/* Failed to WP a pgd range abort */
+		if (ret < 0)
+			goto out;
+		addr = pgdir_end;
+	}
+	ret = 0;
+	/* Flush TLBs, >= ARMv7 variant uses hardware broadcast not IPIs */
+	kvm_flush_remote_tlbs(kvm);
+out:
+	spin_unlock(&kvm->mmu_lock);
+	return ret;
+}
+
 static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 			  struct kvm_memory_slot *memslot,
 			  unsigned long fault_status)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 03a0381..1d11912 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -184,7 +184,10 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
 	return called;
 }
 
-void kvm_flush_remote_tlbs(struct kvm *kvm)
+/* Architectures like >= ARMv7 hardware broadcast TLB invalidations and don't
+ * use IPIs.
+ */
+void __weak kvm_flush_remote_tlbs(struct kvm *kvm)
 {
 	long dirty_count = kvm->tlbs_dirty;
 
-- 
1.7.9.5