[PATCH 3/5] live migration support for VM dirty log management

[Mario Smarduch <m.smarduch@samsung.com>]

Add support for dirty bitmap management. Wanted to make it generic but function
does a couple things different then the x86 version.


Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>
---
 arch/arm/include/asm/kvm_host.h |    3 ++
 arch/arm/kvm/arm.c              |   71 ++++++++++++++++++++++++++++++++++++++-
 arch/arm/kvm/mmu.c              |   53 +++++++++++++++++++++++++++++
 3 files changed, 126 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 7ac1fdc..16ed4e4 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -230,5 +230,8 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *, u64 regid, u64 value);
 
 void kvm_tlb_flush_vm(struct kvm *kvm);
 void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
+void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
+		struct kvm_memory_slot *slot,
+		gfn_t gfn_offset, unsigned long mask);
 
 #endif /* __ARM_KVM_HOST_H__ */
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 7714cc6..7882343 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -785,9 +785,78 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 	}
 }
 
+
+/**
+ * kvm_mmu_slot_remove_access - retrieves the log of dirty pages for a memslot.
+ *	It's itteratively during migration to retrieve pages written since
+ *	last call. In the process write protects ptes that are dirty for next
+ *	time, holds the mmu_lock while write protecting dirty pages.
+ *
+ * @kvm:        The KVM pointer
+ * @log:        Bitmap of dirty pages return.
+ */
 int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
 {
-	return -EINVAL;
+	int r;
+	struct kvm_memory_slot *memslot;
+	unsigned long n, i;
+	unsigned long *dirty_bitmap;
+	unsigned long *dirty_bitmap_buffer;
+	bool is_dirty = false;
+	gfn_t offset;
+
+	mutex_lock(&kvm->slots_lock);
+	r = -EINVAL;
+
+	/* Return with error code will cause migration to abort, this happens
+	 * when initial write protection of VM to manage dirty pages fails
+	 */
+	if (kvm->arch.migration_in_progress == -1)
+		goto out;
+
+	if (log->slot >= KVM_USER_MEM_SLOTS)
+		goto out;
+
+	memslot = id_to_memslot(kvm->memslots, log->slot);
+	dirty_bitmap = memslot->dirty_bitmap;
+
+	r = -ENOENT;
+	if (!dirty_bitmap)
+		goto out;
+
+	n = kvm_dirty_bitmap_bytes(memslot);
+	dirty_bitmap_buffer = dirty_bitmap + n / sizeof(long);
+	memset(dirty_bitmap_buffer, 0, n);
+
+	spin_lock(&kvm->mmu_lock);
+	for (i = 0; i < n / sizeof(long); i++) {
+		unsigned long mask;
+
+		if (!dirty_bitmap[i])
+			continue;
+
+		is_dirty = true;
+		offset = i * BITS_PER_LONG;
+		kvm_mmu_write_protect_pt_masked(kvm, memslot, offset,
+							dirty_bitmap[i]);
+		mask = dirty_bitmap[i];
+		dirty_bitmap_buffer[i] = mask;
+		dirty_bitmap[i] = 0;
+	}
+
+	if (is_dirty)
+		kvm_tlb_flush_vm(kvm);
+
+	spin_unlock(&kvm->mmu_lock);
+	r = -EFAULT;
+
+	if (copy_to_user(log->dirty_bitmap, dirty_bitmap_buffer, n))
+		goto out;
+
+	r = 0;
+out:
+	mutex_unlock(&kvm->slots_lock);
+	return r;
 }
 
 static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm,
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index b85ab56..47bec1c 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -773,6 +773,59 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
 	spin_unlock(&kvm->mmu_lock);
 }
 
+
+/**
+ * kvm_mmu_write_protected_pt_masked - after migration thread write protects
+ *  the entire VM address space itterative calls are made to get diry pages
+ *  as the VM pages are being migrated. New dirty pages may be subset
+ *  of initial WPed VM or new writes faulted in. Here write protect new
+ *  dirty pages again in preparation of next dirty log read. This function is
+ *  called as a result KVM_GET_DIRTY_LOG ioctl, to determine what pages
+ *  need to be migrated.
+ *   'kvm->mmu_lock' must be  held to protect against concurrent modification
+ *   of page tables (2nd stage fault, mmu modifiers, device writes)
+ *
+ * @kvm:        The KVM pointer
+ * @slot:	The memory slot the dirty log is retrieved for
+ * @gfn_offset: The gfn offset in memory slot
+ * @mask:       The mask of dirty pages at offset 'gnf_offset in this memory
+ *              slot to be writ protect
+ */
+
+void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
+		struct kvm_memory_slot *slot,
+		gfn_t gfn_offset, unsigned long mask)
+{
+	phys_addr_t ipa;
+	pgd_t *pgdp = kvm->arch.pgd, *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte, new_pte;
+
+	/* walk set bits in the mask and write protect corresponding pages */
+	while (mask) {
+		ipa = (slot->base_gfn + gfn_offset + __ffs(mask)) << PAGE_SHIFT;
+		pgd = pgdp + pgd_index(ipa);
+		if (!pgd_present(*pgd))
+			goto update_mask;
+		pud = pud_offset(pgd, ipa);
+		if (!pud_present(*pud))
+			goto update_mask;
+		pmd = pmd_offset(pud, ipa);
+		if (!pmd_present(*pmd))
+			goto update_mask;
+		pte = pte_offset_kernel(pmd, ipa);
+		if (!pte_present(*pte))
+			goto update_mask;
+		if ((*pte & L_PTE_S2_RDWR) == L_PTE_S2_RDONLY)
+			goto update_mask;
+		new_pte = pfn_pte(pte_pfn(*pte), PAGE_S2);
+		*pte = new_pte;
+update_mask:
+		mask &= mask - 1;
+	}
+}
+
 static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 			  struct kvm_memory_slot *memslot,
 			  unsigned long fault_status)
-- 
1.7.9.5