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

From: Paolo Bonzini <pbonzini@redhat.com>
To: Yang Weijiang <weijiang.yang@intel.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	jmattson@google.com, sean.j.christopherson@intel.com
Cc: yu.c.zhang@linux.intel.com, alazar@bitdefender.com, edwin.zhai@intel.com
Subject: Re: [PATCH v7 1/9] Documentation: Introduce EPT based Subpage Protection and related ioctls
Date: Thu, 21 Nov 2019 11:02:56 +0100	[thread overview]
Message-ID: <dbf1f124-7864-b1e8-fae3-49448372d502@redhat.com> (raw)
In-Reply-To: <20191119084949.15471-2-weijiang.yang@intel.com>

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);

Thanks,

Paolo