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SubjectRe: x86/sgx: uapi change proposal
On Wed, Dec 19, 2018 at 06:58:48PM -0800, Andy Lutomirski wrote:
> > On Dec 19, 2018, at 6:45 AM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> >
> >> On Wed, Dec 19, 2018 at 09:36:16AM +0000, Jethro Beekman wrote:
>
> > I agree with Jethro, passing the enclave_fd as a param is obnoxious.
> > And it means the user needs to open /dev/sgx to do anything with an
> > enclave fd, e.g. the enclave fd might be passed to a builder thread,
> > it shouldn't also need the device fd.
> >
> > E.g.:
> >
> > sgx_fd = open("/dev/sgx", O_RDWR);
> > BUG_ON(sgx_fd < 0);
> >
> > enclave_fd = ioctl(sgx_fd, SGX_ENCLAVE_CREATE, &ecreate);
> > BUG_ON(enclave_fd < 0);
> >
> > ret = ioctl(enclave_fd, SGX_ENCLAVE_ADD_PAGE, &eadd);
> > BUG_ON(ret);
> >
> > ...
> >
> > ret = ioctl(enclave_fd, SGX_ENCLAVE_INIT, &einit);
> > BUG_ON(ret);
> >
> > ...
> >
> > close(enclave_fd);
> > close(sgx_fd);
> >
> >
> > Take a look at virt/kvm/kvm_main.c to see how KVM manages anon inodes
> > and ioctls for VMs and vCPUs.
>
> Can one of you explain why SGX_ENCLAVE_CREATE is better than just
> opening a new instance of /dev/sgx for each encalve?

Directly associating /dev/sgx with an enclave means /dev/sgx can't be
used to provide ioctl()'s for other SGX-related needs, e.g. to mmap()
raw EPC and expose it a VM. Proposed layout in the link below. I'll
also respond to Jarkko's question about exposing EPC through /dev/sgx
instead of having KVM allocate it on behalf of the VM.

https://lkml.kernel.org/r/20181218185349.GC30082@linux.intel.com

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