Re: [PATCH 2/2] x86/sgx: account backing pages

[Dave Hansen <dave.hansen@intel.com>]

On 12/28/21 3:37 PM, Jarkko Sakkinen wrote:
> On Mon, Dec 20, 2021 at 09:46:40AM -0800, Kristen Carlson Accardi wrote:
>> +int sgx_encl_lookup_backing(struct sgx_encl *encl, unsigned long page_index,
>> +			    struct sgx_backing *backing)
>> +{
>> +	return sgx_encl_get_backing(encl, page_index, backing);
>> +}
> Is this wrapping necessary?

Yes, I think so.

> Also, there is ambiguous terminology:
> 
> 1. Local function: "get_backing"
> 2. Exported function: "lookup_backing"

I'm not sure what you're getting at.

There are three important things that you do with backing storage:

1. Allocate it
2. Find it
3. De-allocate (free) it

Right now, the code has a pattern where it does:

	get_backing();
	// do something
	put_backing();

That sure as heck looks like it is allocating and freeing it.  But, it's
actually *maybe* doing an allocation.  The "find it" path also looks
*EXACTLY* the same as the actual allocation path.  You might also recall
that the original code didn't even *have* a (real) free path.

The "wrapping" is really just naming the two different operations that
use the "get" function: lookup and allocate.  It's not just wrapping,
it's clarify the logical behavior.