Re: [PATCH v10 060/108] KVM: Add functions to set GFN to private or shared

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 10/30/2022 2:23 PM, isaku.yamahata@intel.com wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.com>
> 
> TDX KVM support needs to track whether GFN is private or shared.  Introduce
> functions to set whether GFN is private or shared and pre-allocate memory
> for xarray.
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
>   include/linux/kvm_host.h | 11 ++++++
>   virt/kvm/kvm_main.c      | 74 ++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 85 insertions(+)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index a0b64308d240..fac07886ab39 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2307,9 +2307,20 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
>   #define KVM_MEM_ATTR_PRIVATE	0x0002
>   
>   #ifdef __KVM_HAVE_ARCH_UPDATE_MEM_ATTR
> +/* memory attr on [start, end) */
> +int kvm_vm_reserve_mem_attr(struct kvm *kvm, gfn_t start, gfn_t end);
> +int kvm_vm_set_mem_attr(struct kvm *kvm, int attr, gfn_t start, gfn_t end);
>   void kvm_arch_update_mem_attr(struct kvm *kvm, struct kvm_memory_slot *slot,
>   			      unsigned int attr, gfn_t start, gfn_t end);
>   #else
> +static inline int kvm_vm_reserve_mem_attr(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	return -EOPNOTSUPP;
> +}
> +static inline int kvm_vm_set_mem_attr(struct kvm *kvm, int attr, gfn_t start, gfn_t end)
> +{
> +	return -EOPNOTSUPP;
> +}
>   static inline void kvm_arch_update_mem_attr(struct kvm *kvm,
>   					    struct kvm_memory_slot *slot,
>   					    unsigned int attr,
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 9f82b03a8118..f0e77b65939b 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1121,6 +1121,80 @@ static inline void kvm_restrictedmem_unregister(struct kvm_memory_slot *slot)
>   					  &slot->notifier);
>   }
>   
> +/*
> + * Reserve memory for [start, end) so that the next set oepration won't fail
> + * with -ENOMEM.
> + */
> +int kvm_vm_reserve_mem_attr(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	int r = 0;
> +	gfn_t gfn;
> +
> +	xa_lock(&kvm->mem_attr_array);
> +	for (gfn = start; gfn < end; gfn++) {
> +		r = __xa_insert(&kvm->mem_attr_array, gfn, NULL, GFP_KERNEL_ACCOUNT);
> +		if (r == -EBUSY)
> +			r = 0;
> +		if (r)
> +			break;
> +	}
> +	xa_unlock(&kvm->mem_attr_array);
> +
> +	return r;
> +}
> +EXPORT_SYMBOL_GPL(kvm_vm_reserve_mem_attr);
> +
> +/* Set memory attr for [start, end) */
> +int kvm_vm_set_mem_attr(struct kvm *kvm, int attr, gfn_t start, gfn_t end)
> +{
> +	void *entry;
> +	gfn_t gfn;
> +	int r;
> +	int i;
> +
> +	/* By default, the entry is private. */
> +	switch (attr) {
> +	case KVM_MEM_ATTR_PRIVATE:
> +		entry = NULL;
> +		break;
> +	case KVM_MEM_ATTR_SHARED:
> +		entry = xa_mk_value(KVM_MEM_ATTR_SHARED);
> +		break;
> +	default:
> +		WARN_ON_ONCE(1);
> +		return -EINVAL;
> +	}
> +
> +	WARN_ON_ONCE(start >= end);
> +	for (gfn = start; gfn < end; gfn++) {
> +		r = xa_err(xa_store(&kvm->mem_attr_array, gfn, entry,
> +				    GFP_KERNEL_ACCOUNT));
> +		if (r)
> +			break;
> +	}
> +	if (start >= gfn)
> +		return r;
> +
> +	end = gfn;
> +	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> +		struct kvm_memslot_iter iter;
> +		struct kvm_memory_slot *slot;
> +		struct kvm_memslots *slots;
> +
> +		slots = __kvm_memslots(kvm, i);
> +		kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {

slot needs to be set as

			slot = iter.slot;

> +			gfn_t s = max(start, slot->base_gfn);
> +			gfn_t e = min(end, slot->base_gfn + slot->npages);
> +
> +			WARN_ON_ONCE(s >= e);
> +			kvm_arch_update_mem_attr(kvm, slot, attr, s, e);
> +		}
> +	}
> +
> +	return r;
> +}
> +EXPORT_SYMBOL_GPL(kvm_vm_set_mem_attr);
> +
>   #else /* !CONFIG_HAVE_KVM_RESTRICTED_MEM */
>   
>   static inline void kvm_restrictedmem_register(struct kvm_memory_slot *slot)