[PATCH] kvm: Fix memory slot generation updates

[PATCH] kvm: Fix memory slot generation updates

[Alex Williamson]

Previous patch "kvm: Minor memory slot optimization" overlooked the
generation field of the memory slots.  Re-using the original memory
slots left us with with two slightly different memory slots with the
same generation.  To fix this, make update_memslots() take a new
parameter to specify the last generation.  This also makes generation
management more explicit to avoid such problems in the future.

Reported-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 include/linux/kvm_host.h |    3 ++-
 virt/kvm/kvm_main.c      |    9 +++++----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 32fdc45..cbe0d68 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -428,7 +428,8 @@ void kvm_exit(void);
 
 void kvm_get_kvm(struct kvm *kvm);
 void kvm_put_kvm(struct kvm *kvm);
-void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new);
+void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new,
+		     u64 last_generation);
 
 static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
 {
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index bd31096..14cbae8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -672,7 +672,8 @@ static void sort_memslots(struct kvm_memslots *slots)
 		slots->id_to_index[slots->memslots[i].id] = i;
 }
 
-void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new)
+void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new,
+		     u64 last_generation)
 {
 	if (new) {
 		int id = new->id;
@@ -684,7 +685,7 @@ void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new)
 			sort_memslots(slots);
 	}
 
-	slots->generation++;
+	slots->generation = last_generation + 1;
 }
 
 static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
@@ -819,7 +820,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		slot = id_to_memslot(slots, mem->slot);
 		slot->flags |= KVM_MEMSLOT_INVALID;
 
-		update_memslots(slots, NULL);
+		update_memslots(slots, NULL, kvm->memslots->generation);
 
 		old_memslots = kvm->memslots;
 		rcu_assign_pointer(kvm->memslots, slots);
@@ -867,7 +868,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		memset(&new.arch, 0, sizeof(new.arch));
 	}
 
-	update_memslots(slots, &new);
+	update_memslots(slots, &new, kvm->memslots->generation);
 	old_memslots = kvm->memslots;
 	rcu_assign_pointer(kvm->memslots, slots);
 	synchronize_srcu_expedited(&kvm->srcu);

Re: [PATCH] kvm: Fix memory slot generation updates

[Gleb Natapov]

On Fri, Dec 21, 2012 at 08:20:16AM -0700, Alex Williamson wrote:
> Previous patch "kvm: Minor memory slot optimization" overlooked the
> generation field of the memory slots.  Re-using the original memory
> slots left us with with two slightly different memory slots with the
> same generation.  To fix this, make update_memslots() take a new
> parameter to specify the last generation.  This also makes generation
> management more explicit to avoid such problems in the future.
> 
> Reported-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Applied, thanks. What about this small cleanup on to of the patch:


diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 14cbae8..e45c20c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -702,6 +702,17 @@ static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
 	return 0;
 }
 
+static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
+		struct kvm_memslots *slots, struct kvm_memory_slot *new)
+{
+	struct kvm_memslots *old_memslots = kvm->memslots;
+
+	update_memslots(slots, new, kvm->memslots->generation);
+	rcu_assign_pointer(kvm->memslots, slots);
+	synchronize_srcu_expedited(&kvm->srcu);
+	return old_memslots; 
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -820,11 +831,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		slot = id_to_memslot(slots, mem->slot);
 		slot->flags |= KVM_MEMSLOT_INVALID;
 
-		update_memslots(slots, NULL, kvm->memslots->generation);
+		old_memslots = install_new_memslots(kvm, slots, NULL);
 
-		old_memslots = kvm->memslots;
-		rcu_assign_pointer(kvm->memslots, slots);
-		synchronize_srcu_expedited(&kvm->srcu);
 		/* slot was deleted or moved, clear iommu mapping */
 		kvm_iommu_unmap_pages(kvm, &old);
 		/* From this point no new shadow pages pointing to a deleted,
@@ -868,10 +876,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		memset(&new.arch, 0, sizeof(new.arch));
 	}
 
-	update_memslots(slots, &new, kvm->memslots->generation);
-	old_memslots = kvm->memslots;
-	rcu_assign_pointer(kvm->memslots, slots);
-	synchronize_srcu_expedited(&kvm->srcu);
+	old_memslots = install_new_memslots(kvm, slots, &new);
 
 	kvm_arch_commit_memory_region(kvm, mem, old, user_alloc);
 
--
			Gleb.

Re: [PATCH] kvm: Fix memory slot generation updates

[Takuya Yoshikawa]

On Sun, 23 Dec 2012 10:55:06 +0200
Gleb Natapov <gleb@redhat.com> wrote:

> Applied, thanks. What about this small cleanup on to of the patch:

Looks nice!  Hope to see this applied as well.

Thanks,
	Takuya

> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 14cbae8..e45c20c 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -702,6 +702,17 @@ static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
>  	return 0;
>  }
>  
> +static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
> +		struct kvm_memslots *slots, struct kvm_memory_slot *new)
> +{
> +	struct kvm_memslots *old_memslots = kvm->memslots;
> +
> +	update_memslots(slots, new, kvm->memslots->generation);
> +	rcu_assign_pointer(kvm->memslots, slots);
> +	synchronize_srcu_expedited(&kvm->srcu);
> +	return old_memslots; 
> +}
> +
>  /*
>   * Allocate some memory and give it an address in the guest physical address
>   * space.
> @@ -820,11 +831,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  		slot = id_to_memslot(slots, mem->slot);
>  		slot->flags |= KVM_MEMSLOT_INVALID;
>  
> -		update_memslots(slots, NULL, kvm->memslots->generation);
> +		old_memslots = install_new_memslots(kvm, slots, NULL);
>  
> -		old_memslots = kvm->memslots;
> -		rcu_assign_pointer(kvm->memslots, slots);
> -		synchronize_srcu_expedited(&kvm->srcu);
>  		/* slot was deleted or moved, clear iommu mapping */
>  		kvm_iommu_unmap_pages(kvm, &old);
>  		/* From this point no new shadow pages pointing to a deleted,
> @@ -868,10 +876,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  		memset(&new.arch, 0, sizeof(new.arch));
>  	}
>  
> -	update_memslots(slots, &new, kvm->memslots->generation);
> -	old_memslots = kvm->memslots;
> -	rcu_assign_pointer(kvm->memslots, slots);
> -	synchronize_srcu_expedited(&kvm->srcu);
> +	old_memslots = install_new_memslots(kvm, slots, &new);
>  
>  	kvm_arch_commit_memory_region(kvm, mem, old, user_alloc);
>  
> --
> 			Gleb.


-- 
Takuya Yoshikawa <takuya.yoshikawa@gmail.com>

Re: [PATCH] kvm: Fix memory slot generation updates

[Alex Williamson]

On Sun, 2012-12-23 at 10:55 +0200, Gleb Natapov wrote:
> On Fri, Dec 21, 2012 at 08:20:16AM -0700, Alex Williamson wrote:
> > Previous patch "kvm: Minor memory slot optimization" overlooked the
> > generation field of the memory slots.  Re-using the original memory
> > slots left us with with two slightly different memory slots with the
> > same generation.  To fix this, make update_memslots() take a new
> > parameter to specify the last generation.  This also makes generation
> > management more explicit to avoid such problems in the future.
> > 
> > Reported-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> Applied, thanks. What about this small cleanup on to of the patch:

Nice cleanup

Reviewed-by: Alex Williamson <alex.williamson@redhat.com>

> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 14cbae8..e45c20c 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -702,6 +702,17 @@ static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
>  	return 0;
>  }
>  
> +static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
> +		struct kvm_memslots *slots, struct kvm_memory_slot *new)
> +{
> +	struct kvm_memslots *old_memslots = kvm->memslots;
> +
> +	update_memslots(slots, new, kvm->memslots->generation);
> +	rcu_assign_pointer(kvm->memslots, slots);
> +	synchronize_srcu_expedited(&kvm->srcu);
> +	return old_memslots; 
> +}
> +
>  /*
>   * Allocate some memory and give it an address in the guest physical address
>   * space.
> @@ -820,11 +831,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  		slot = id_to_memslot(slots, mem->slot);
>  		slot->flags |= KVM_MEMSLOT_INVALID;
>  
> -		update_memslots(slots, NULL, kvm->memslots->generation);
> +		old_memslots = install_new_memslots(kvm, slots, NULL);
>  
> -		old_memslots = kvm->memslots;
> -		rcu_assign_pointer(kvm->memslots, slots);
> -		synchronize_srcu_expedited(&kvm->srcu);
>  		/* slot was deleted or moved, clear iommu mapping */
>  		kvm_iommu_unmap_pages(kvm, &old);
>  		/* From this point no new shadow pages pointing to a deleted,
> @@ -868,10 +876,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  		memset(&new.arch, 0, sizeof(new.arch));
>  	}
>  
> -	update_memslots(slots, &new, kvm->memslots->generation);
> -	old_memslots = kvm->memslots;
> -	rcu_assign_pointer(kvm->memslots, slots);
> -	synchronize_srcu_expedited(&kvm->srcu);
> +	old_memslots = install_new_memslots(kvm, slots, &new);
>  
>  	kvm_arch_commit_memory_region(kvm, mem, old, user_alloc);
>  
> --
> 			Gleb.