KVM: Add generic support for dirty page logging

kvm_get_dirty_log() provides generic handling of dirty bitmap, currently reused
by several architectures. Building on that we intrdoduce
kvm_get_dirty_log_protect() adding write protection to mark these pages dirty
for future write access, before next KVM_GET_DIRTY_LOG ioctl call from user
space.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 26f1060..3b934cc 100644 (file)
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -611,6 +611,15 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext);
 
 int kvm_get_dirty_log(struct kvm *kvm,
                        struct kvm_dirty_log *log, int *is_dirty);
+
+int kvm_get_dirty_log_protect(struct kvm *kvm,
+                       struct kvm_dirty_log *log, bool *is_dirty);
+
+void kvm_arch_mmu_write_protect_pt_masked(struct kvm *kvm,
+                                       struct kvm_memory_slot *slot,
+                                       gfn_t gfn_offset,
+                                       unsigned long mask);
+
 int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
                                struct kvm_dirty_log *log);
 

diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 3796a21..314950c 100644 (file)
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -40,3 +40,9 @@ config KVM_VFIO
 
 config HAVE_KVM_ARCH_TLB_FLUSH_ALL
        bool
+
+config HAVE_KVM_ARCH_DIRTY_LOG_PROTECT
+       bool
+
+config KVM_GENERIC_DIRTYLOG_READ_PROTECT
+       bool

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d03bd22..246cf29 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -995,6 +995,86 @@ out:
 }
 EXPORT_SYMBOL_GPL(kvm_get_dirty_log);
 
+#ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
+/**
+ * kvm_get_dirty_log_protect - get a snapshot of dirty pages, and if any pages
+ *     are dirty write protect them for next write.
+ * @kvm:       pointer to kvm instance
+ * @log:       slot id and address to which we copy the log
+ * @is_dirty:  flag set if any page is dirty
+ *
+ * We need to keep it in mind that VCPU threads can write to the bitmap
+ * concurrently. So, to avoid losing track of dirty pages we keep the
+ * following order:
+ *
+ *    1. Take a snapshot of the bit and clear it if needed.
+ *    2. Write protect the corresponding page.
+ *    3. Copy the snapshot to the userspace.
+ *    4. Upon return caller flushes TLB's if needed.
+ *
+ * Between 2 and 4, the guest may write to the page using the remaining TLB
+ * entry.  This is not a problem because the page is reported dirty using
+ * the snapshot taken before and step 4 ensures that writes done after
+ * exiting to userspace will be logged for the next call.
+ *
+ */
+int kvm_get_dirty_log_protect(struct kvm *kvm,
+                       struct kvm_dirty_log *log, bool *is_dirty)
+{
+       struct kvm_memory_slot *memslot;
+       int r, i;
+       unsigned long n;
+       unsigned long *dirty_bitmap;
+       unsigned long *dirty_bitmap_buffer;
+
+       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);
+       *is_dirty = false;
+       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_arch_mmu_write_protect_pt_masked(kvm, memslot, offset,
+                                                               mask);
+       }
+
+       spin_unlock(&kvm->mmu_lock);
+
+       r = -EFAULT;
+       if (copy_to_user(log->dirty_bitmap, dirty_bitmap_buffer, n))
+               goto out;
+
+       r = 0;
+out:
+       return r;
+}
+EXPORT_SYMBOL_GPL(kvm_get_dirty_log_protect);
+#endif
+
 bool kvm_largepages_enabled(void)
 {
        return largepages_enabled;