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

[Yang Weijiang]

On Thu, Nov 21, 2019 at 11:02:56AM +0100, Paolo Bonzini wrote:
> On 19/11/19 09:49, Yang Weijiang wrote:
> > +
> > +#define SUBPAGE_MAX_BITMAP   64
> 
> Please rename this to KVM_SUBPAGE_MAX_PAGES
>
OK.
> > +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.
> 
Cool, thanks for the suggestion!

> > +	__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);
>
Sure, will make the change. thank you!

> Thanks,
> 
> Paolo