Re: [PATCH v7 1/9] Documentation: Introduce EPT based Subpage Protection and related ioctls

From: Paolo Bonzini
Date: Thu Nov 21 2019 - 05:03:02 EST

On 19/11/19 09:49, Yang Weijiang wrote:
> +
> +#define SUBPAGE_MAX_BITMAP 64

Please rename this to KVM_SUBPAGE_MAX_PAGES

> +struct kvm_subpage_info {
> + __u64 gfn; /* the first page gfn of the contiguous pages */
> + __u64 npages; /* number of 4K pages */

This can be

u32 npages;
u32 flags;

Check that the flags are 0, and fail the ioctl if they aren't. This
will make it easy to extend the API in the future.

> + __u32 access_map[SUBPAGE_MAX_BITMAP]; /* sub-page write-access bitmap array */
> +};

Please make this access_map[0], since the number of entries actually
depends on npages.

Likewise, kvm_arch_vm_ioctl should read the header first, then allocate
memory for the access_map and read into it. It's probably simpler if
you make kvm_vm_ioctl_get_subpages/kvm_vm_ioctl_set_subpages take
parameters like

int kvm_vm_ioctl_get_subpages(struct kvm *kvm, u64 gfn, u32 npages,
u32 *access_map);
int kvm_vm_ioctl_set_subpages(struct kvm *kvm, u64 gfn, u32 npages,
u32 *access_map);