Re: [PATCH for_v22] selftests/x86/sgx: Ensure SECS base (ELRANGE) is naturally aligned

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Fri, Aug 09, 2019 at 05:30:51PM -0700, Sean Christopherson wrote:
> Manually align ELRANGE now that the kernel doesn't automatically do so
> for SGX mappings.  To guarantee mmap() returns a region that can be
> naturally aligned, temporarily map 2x the enclave size and do fancy
> arithmetic to naturally align the base.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>

Thank you.

I fine-tuned the calculations a bit:

area = mmap(NULL, secs->size * 2, PROT_NONE, MAP_SHARED, dev_fd, 0);
if (area == MAP_FAILED) {
	perror("mmap");
	return false;
}

secs->base = ((uint64_t)area + secs->size - 1) & ~(secs->size - 1);

munmap(area, secs->base - (uint64_t)area);
munmap((void *)(secs->base + secs->size),
       (uint64_t)area + secs->size - secs->base);

/Jarkko