Re: [RFC PATCH 5/6] kvm: Re-introduce memslots->nmemslots

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Dec 03, 2012 at 04:39:36PM -0700, Alex Williamson wrote:
> struct kvm_memory_slot is currently 52 bytes (LP64), not counting the
> arch data.  On x86 this means the memslot array to support a tiny 32+3
> entries (user+private) is over 2k.  We'd like to support more slots
> so that we can support more assigned devices, but it doesn't make
> sense to penalize everyone by using a statically allocated array.
> This allows us to start introducing a grow-able array.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
>  arch/ia64/kvm/kvm-ia64.c     |    2 +-
>  arch/powerpc/kvm/book3s_hv.c |    2 +-
>  arch/x86/kvm/vmx.c           |    1 +
>  arch/x86/kvm/x86.c           |    4 +++-
>  include/linux/kvm_host.h     |    9 ++++++---
>  virt/kvm/kvm_main.c          |   10 ++++++----
>  6 files changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
> index 012e5dd..96401b5 100644
> --- a/arch/ia64/kvm/kvm-ia64.c
> +++ b/arch/ia64/kvm/kvm-ia64.c
> @@ -1836,7 +1836,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
>  
>  	memslot = id_to_memslot(kvm->memslots, log->slot);
>  	r = -ENOENT;
> -	if (!memslot->dirty_bitmap)
> +	if (!memslots || !memslot->dirty_bitmap)
>  		goto out;
>  
>  	kvm_ia64_sync_dirty_log(kvm, memslot);
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 56067db..0417190 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1267,7 +1267,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
>  
>  	memslot = id_to_memslot(kvm->memslots, log->slot);
>  	r = -ENOENT;
> -	if (!memslot->dirty_bitmap)
> +	if (!memslot || !memslot->dirty_bitmap)
>  		goto out;
>  
>  	n = kvm_dirty_bitmap_bytes(memslot);
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 2bb9157..07fdd90 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2751,6 +2751,7 @@ static gva_t rmode_tss_base(struct kvm *kvm)
>  
>  		slots = kvm_memslots(kvm);
>  		slot = id_to_memslot(slots, KVM_PRIVATE_MEM_SLOTS);
> +		BUG_ON(!slot);
>  		base_gfn = slot->base_gfn + slot->npages - 3;
>  
>  		return base_gfn << PAGE_SHIFT;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8765485..53fe9b2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3139,9 +3139,11 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
>  		goto out;
>  
>  	memslot = id_to_memslot(kvm->memslots, log->slot);
> +	r = -ENOENT;
> +	if (!memslot)
> +		goto out;
>  
>  	dirty_bitmap = memslot->dirty_bitmap;
> -	r = -ENOENT;
>  	if (!dirty_bitmap)
>  		goto out;
>  
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 7b3d5c4..1955a4e 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -313,6 +313,7 @@ struct kvm_irq_routing_table {};
>   * to get the memslot by its id.
>   */
>  struct kvm_memslots {
> +	int nmemslots;
>  	u64 generation;
>  	struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
>  };
> @@ -397,7 +398,7 @@ static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i)
>  
>  #define kvm_for_each_memslot(memslot, slots)	\
>  	for (memslot = &slots->memslots[0];	\
> -	      memslot < slots->memslots + KVM_MEM_SLOTS_NUM && memslot->npages;\
> +	      memslot < slots->memslots + slots->nmemslots && memslot->npages;\
>  		memslot++)
>  
>  int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id);
> @@ -424,10 +425,12 @@ static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
>  static inline struct kvm_memory_slot *
>  id_to_memslot(struct kvm_memslots *slots, int id)
>  {
> -	int index = slots->memslots[id].id_to_index;
>  	struct kvm_memory_slot *slot;
>  
> -	slot = &slots->memslots[index];
> +	if (id >= slots->nmemslots)
> +		return NULL;
> +
> +	slot = &slots->memslots[slots->memslots[id].id_to_index];
>  
>  	WARN_ON(slot->id != id);
>  	return slot;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 3ce2664..ebd3960 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -444,7 +444,9 @@ static void kvm_init_memslots_id(struct kvm *kvm)
>  	int i;
>  	struct kvm_memslots *slots = kvm->memslots;
>  
> -	for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
> +	slots->nmemslots = KVM_MEM_SLOTS_NUM;
> +
> +	for (i = 0; i < kvm->memslots->nmemslots; i++)
>  		slots->memslots[i].id_to_index = slots->memslots[i].id = i;
>  }
>  
> @@ -658,10 +660,10 @@ static void sort_memslots(struct kvm_memslots *slots)
>  {
>  	int i;
>  
> -	sort(slots->memslots, KVM_MEM_SLOTS_NUM,
> +	sort(slots->memslots, slots->nmemslots,
>  	      sizeof(struct kvm_memory_slot), cmp_memslot, NULL);
>  
> -	for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
> +	for (i = 0; i < slots->nmemslots; i++)
>  		slots->memslots[slots->memslots[i].id].id_to_index = i;
>  }
>  
> @@ -898,7 +900,7 @@ int kvm_get_dirty_log(struct kvm *kvm,
>  
>  	memslot = id_to_memslot(kvm->memslots, log->slot);
>  	r = -ENOENT;
> -	if (!memslot->dirty_bitmap)
> +	if (!memslot || !memslot->dirty_bitmap)
>  		goto out;
>  
>  	n = kvm_dirty_bitmap_bytes(memslot);

I suppose this should be checked earlier, not at id_to_memslot time.
eg for kvm_get_dirty_log at 

        r = -EINVAL;
        if (log->slot >= KVM_MEMORY_SLOTS)
                goto out;

time