Re: [PATCH v2 2/2] x86/sgx: account backing pages

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Jan 14, 2022 at 09:55:51AM -0800, Dave Hansen wrote:
> On 1/14/22 9:51 AM, 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);
> >>> +}
> >> IMHO, sgx_encl_backing() should be open-coded here.
> > I can understand your hesitation, but I agree with Dave here that
> > wrapping the function makes the code more clear. I would prefer to keep
> > this the way it is.
> 
> I'd also like to see sgx_encl_lookup_backing() and
> sgx_encl_alloc_backing() diverge more in the future.
> 
> For instance, sgx_encl_alloc_backing() could ensure that the page does
> not exist in the file before doing the sgx_encl_get_backing() call.
> This would ensure that it truly *does* allocate a page and does not just
> return a previously-allocated page.
> 
> sgx_encl_lookup_backing() could ensure the opposite: that the page
> *DOES* exist in the file before doing the sgx_encl_get_backing() call.
> This would ensure that it does not allocate a page in a case where we
> expected an old, existing page to be present.

Would it be a too big tretch to add these and make the whole scheme
fully legit? Does not sound like an extremely huge stretch and there is now
a full cycle amount of time make it happen before 5.18 merge window.

/Jarkko