Re: [PATCH v16 18/22] platform/x86: Intel SGX driver

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Tue, 2018-11-06 at 15:45 +0200, Jarkko Sakkinen wrote:
> Intel Software Guard eXtensions (SGX) is a set of CPU instructions that
> can be used by applications to set aside private regions of code and
> data. The code outside the enclave is disallowed to access the memory
> inside the enclave by the CPU access control.
> 
> SGX driver provides a ioctl API for loading and initializing enclaves.
> Address range for enclaves is reserved with mmap() and they are
> destroyed with munmap(). Enclave construction, measurement and
> initialization is done with the provided the ioctl API.

...

> +struct sgx_encl {
> +	unsigned int flags;
> +	uint64_t attributes;
> +	uint64_t xfrm;
> +	unsigned int page_cnt;
> +	unsigned int secs_child_cnt;
> +	struct mutex lock;
> +	struct mm_struct *mm;
> +	struct file *backing;

Is there any particular reason why the kernel manages the backing for
the enclave and the PCMDs?  Could we have userspace provide the backing
either through the ECREATE ioctl() or maybe a completely new ioctl(),
e.g. to give userspace the option to back the enclave with a NVDIMM
instead of RAM?  A separate ioctl() with control flags might give us
some flexibility in the future, e.g. maybe there are use cases where
userspace would prefer to kill enclaves rather than swap EPC.

> +	struct kref refcount;
> +	unsigned long base;
> +	unsigned long size;
> +	unsigned long ssaframesize;
> +	struct radix_tree_root page_tree;
> +	struct list_head add_page_reqs;
> +	struct work_struct add_page_work;
> +	struct sgx_encl_page secs;
> +	struct pid *tgid;
> +	struct mmu_notifier mmu_notifier;
> +	struct notifier_block pm_notifier;
> +};