Re: [RFC 21/33] KVM: Pass memory attribute array as a MMU notifier argument

[Sean Christopherson]

On Wed, Nov 08, 2023, Nicolas Saenz Julienne wrote:
> Pass the memory attribute array through struct kvm_mmu_notifier_arg and
> use it in kvm_arch_post_set_memory_attributes() instead of defaulting on
> kvm->mem_attr_array.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenz@xxxxxxxxxx>
> ---
>  arch/x86/kvm/mmu/mmu.c   | 8 ++++----
>  include/linux/kvm_host.h | 5 ++++-
>  virt/kvm/kvm_main.c      | 1 +
>  3 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index c0fd3afd6be5..c2bec2be2ba9 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -7311,6 +7311,7 @@ static bool hugepage_has_attrs(struct xarray *mem_attr_array,
>  bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
>  					 struct kvm_gfn_range *range)
>  {
> +	struct xarray *mem_attr_array = range->arg.mem_attr_array;
>  	unsigned long attrs = range->arg.attributes;
>  	struct kvm_memory_slot *slot = range->slot;
>  	int level;
> @@ -7344,8 +7345,8 @@ bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
>  			 * misaligned address regardless of memory attributes.
>  			 */
>  			if (gfn >= slot->base_gfn) {
> -				if (hugepage_has_attrs(&kvm->mem_attr_array,
> -						       slot, gfn, level, attrs))
> +				if (hugepage_has_attrs(mem_attr_array, slot,
> +						       gfn, level, attrs))

This is wildly broken.  The hugepage tracking is per VM, whereas the attributes
here are per-VTL.  I.e. KVM will (dis)allow hugepages based on whatever VTL last
changed its protections.