[PATCH v6 3/4] live migration support for VM dirty log management

Mario Smarduch
2014-05-15T18:28:25Z

This patch adds support for keeping track of VM dirty pages, by updating
per memslot dirty bitmap and write protecting the page again.

Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>
---
arch/arm/include/asm/kvm_host.h | 3 ++
arch/arm/kvm/arm.c | 5 --
arch/arm/kvm/mmu.c | 98 +++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/x86.c | 86 ----------------------------------
virt/kvm/kvm_main.c | 82 ++++++++++++++++++++++++++++++++
5 files changed, 183 insertions(+), 91 deletions(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 0e55b17..4fef77d 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -238,5 +238,8 @@ u64 kvm_arm_timer_get_reg(struct kvm_vcpu *, u64 regid);
int kvm_arm_timer_set_reg(struct kvm_vcpu *, u64 regid, u64 value);

int 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 1055266..0b847b5 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -777,11 +777,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
}
}

-int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
-{
- return -EINVAL;
-}
-
static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm,
struct kvm_arm_device_addr *dev_addr)
{
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index b71ad27..b939312 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -891,6 +891,104 @@ out:
return ret;
}

+
+/**
+ * kvm_mmu_write_protected_pt_masked - walk mask relative start of memslot and
+ * write protect again for next dirty log read.
+ *
+ * After migration thread write protects entire VM iterative calls are made
+ * to get diry page log. The log is returned and dirty pages are write
+ * protected again. This function is called as a result KVM_GET_DIRTY_LOG
+ * ioctl.
+ * 'kvm->mmu_lock' must be held to protect against concurrent modification
+ * of page tables (2nd stage fault, mmu modifiers, ...)
+ *
+ * @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, next, offset_ipa;
+ pgd_t *pgdp = kvm->arch.pgd, *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *pte;
+ gfn_t gfnofst = slot->base_gfn + gfn_offset;
+ bool crosses_pmd;
+
+ ipa = (gfnofst + __ffs(mask)) << PAGE_SHIFT;
+ offset_ipa = gfnofst << PAGE_SHIFT;
+ next = (gfnofst + (BITS_PER_LONG - 1)) << PAGE_SHIFT;
+
+ /* check if mask width crosses 2nd level page table range, and
+ * possibly 3rd, 4th. If not skip upper table lookups. Unlikely
+ * to be true.
+ */
+ crosses_pmd = ((offset_ipa & PMD_MASK) ^ (next & PMD_MASK)) ? true :
+ false;
+
+ /* If pgd, pud, pmd not present and you cross pmd range check next
+ * index.
+ */
+ pgd = pgdp + pgd_index(ipa);
+ if (unlikely(crosses_pmd && !pgd_present(*pgd))) {
+ pgd = pgdp + pgd_index(next);
+ if (!pgd_present(*pgd))
+ return;
+ }
+
+ pud = pud_offset(pgd, ipa);
+ if (unlikely(crosses_pmd && !pud_present(*pud))) {
+ pud = pud_offset(pgd, next);
+ if (!pud_present(*pud))
+ return;
+ }
+
+ pmd = pmd_offset(pud, ipa);
+ if (unlikely(crosses_pmd && !pmd_present(*pmd))) {
+ pmd = pmd_offset(pud, next);
+ if (!pmd_present(*pmd))
+ return;
+ }
+
+ for (;;) {
+ pte = pte_offset_kernel(pmd, ipa);
+ if (!pte_present(*pte))
+ goto next_ipa;
+
+ if (kvm_s2pte_readonly(pte))
+ goto next_ipa;
+ kvm_set_s2pte_readonly(pte);
+next_ipa:
+ mask &= mask - 1;
+ if (!mask)
+ break;
+
+ /* find next page */
+ ipa = (gfnofst + __ffs(mask)) << PAGE_SHIFT;
+
+ /* skip upper page table lookups */
+ if (!crosses_pmd)
+ continue;
+
+ pgd = pgdp + pgd_index(ipa);
+ if (unlikely(!pgd_present(*pgd)))
+ goto next_ipa;
+ pud = pud_offset(pgd, ipa);
+ if (unlikely(!pud_present(*pud)))
+ goto next_ipa;
+ pmd = pmd_offset(pud, ipa);
+ if (unlikely(!pmd_present(*pmd)))
+ goto next_ipa;
+ }
+}
+
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/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c5582c3..a603ca3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3569,92 +3569,6 @@ static int kvm_vm_ioctl_reinject(struct kvm *kvm,
return 0;
}

-/**
- * kvm_vm_ioctl_get_dirty_log - get and clear the log of dirty pages in a slot
- * @kvm: kvm instance
- * @log: slot id and address to which we copy the log
- *
- * We need to keep it in mind that VCPU threads can write to the bitmap
- * concurrently. So, to avoid losing data, we keep the following order for
- * each bit:
- *
- * 1. Take a snapshot of the bit and clear it if needed.
- * 2. Write protect the corresponding page.
- * 3. Flush TLB's if needed.
- * 4. Copy the snapshot to the userspace.
- *
- * Between 2 and 3, the guest may write to the page using the remaining TLB
- * entry. This is not a problem because the page will be reported dirty at
- * step 4 using the snapshot taken before and step 3 ensures that successive
- * writes will be logged for the next call.
- */
-int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
-{
- int r;
- struct kvm_memory_slot *memslot;
- unsigned long n, i;
- unsigned long *dirty_bitmap;
- unsigned long *dirty_bitmap_buffer;
- bool is_dirty = false;
-
- mutex_lock(&kvm->slots_lock);
-
- r = -EINVAL;
- 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;
- gfn_t offset;
-
- if (!dirty_bitmap[i])
- continue;
-
- is_dirty = true;
-
- mask = xchg(&dirty_bitmap[i], 0);
- dirty_bitmap_buffer[i] = mask;
-
- offset = i * BITS_PER_LONG;
- kvm_mmu_write_protect_pt_masked(kvm, memslot, offset, mask);
- }
-
- spin_unlock(&kvm->mmu_lock);
-
- /* See the comments in kvm_mmu_slot_remove_write_access(). */
- lockdep_assert_held(&kvm->slots_lock);
-
- /*
- * All the TLBs can be flushed out of mmu lock, see the comments in
- * kvm_mmu_slot_remove_write_access().
- */
- if (is_dirty)
- kvm_flush_remote_tlbs(kvm);
-
- 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;
-}
-
int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_event,
bool line_status)
{
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ba25765..d33ac9c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -429,6 +429,88 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
return mmu_notifier_register(&kvm->mmu_notifier, current->mm);
}

+/**
+ * kvm_vm_ioctl_get_dirty_log - get and clear the log of dirty pages in a slot
+ * @kvm: kvm instance
+ * @log: slot id and address to which we copy the log
+ *
+ * Shared by x86 and ARM.
+ *
+ * We need to keep it in mind that VCPU threads can write to the bitmap
+ * concurrently. So, to avoid losing data, we keep the following order for
+ * each bit:
+ *
+ * 1. Take a snapshot of the bit and clear it if needed.
+ * 2. Write protect the corresponding page.
+ * 3. Flush TLB's if needed.
+ * 4. Copy the snapshot to the userspace.
+ *
+ * Between 2 and 3, the guest may write to the page using the remaining TLB
+ * entry. This is not a problem because the page will be reported dirty at
+ * step 4 using the snapshot taken before and step 3 ensures that successive
+ * writes will be logged for the next call.
+ */
+
+int __weak kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
+ struct kvm_dirty_log *log)
+{
+ int r;
+ struct kvm_memory_slot *memslot;
+ unsigned long n, i;
+ unsigned long *dirty_bitmap;
+ unsigned long *dirty_bitmap_buffer;
+ bool is_dirty = false;
+
+ mutex_lock(&kvm->slots_lock);
+
+ r = -EINVAL;
+ 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;
+ gfn_t offset;
+
+ if (!dirty_bitmap[i])
+ continue;
+
+ is_dirty = true;
+
+ mask = xchg(&dirty_bitmap[i], 0);
+ dirty_bitmap_buffer[i] = mask;
+
+ offset = i * BITS_PER_LONG;
+ kvm_mmu_write_protect_pt_masked(kvm, memslot, offset, mask);
+ }
+ if (is_dirty)
+ kvm_flush_remote_tlbs(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;
+}
+
#else /* !(CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER) */

static int kvm_init_mmu_notifier(struct kvm *kvm)
--
1.7.9.5