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SubjectRe: [PATCH v30 08/20] x86/sgx: Add functions to allocate and free EPC pages
On Thu, May 28, 2020 at 10:07:18PM +0300, Jarkko Sakkinen wrote:
> On Thu, May 28, 2020 at 07:16:35PM +0200, Borislav Petkov wrote:
> > Lemme reply to all mails with one. :-)
> > And except those last two. Those are allocating a page from the EPC
> > sections so I'd call them:
> >
> > sgx_try_alloc_page -> sgx_alloc_epc_page_section
> > __sgx_try_alloc_page -> __sgx_alloc_epc_page_section
> >
> > former doing the loop, latter doing the per-section list games.
> sgx_alloc_epc_page_section() is a bit nasty and long name to use for
> grabbing a page. And even the documentation spoke about grabbing before
> this naming discussion. I think it is a great description what is going
> on. Everytime I talk about the subject I talk about grabbing.
> Lets just say that your suggestion, I could not use in a conference
> talk as a verb when I describe what is going on. That function
> signature does not fit to my mouth :-) I would talk about
> grabbing a page.

"allocate an EPC page from the specified section"

It also works if/when we add NUMA awareness, e.g. sgx_alloc_epc_page_node()
means "allocate an EPC page from the specified node". Note that I'm not
inventing these from scratch, simply stealing them from alloc_pages() and
alloc_pages_node(). The section thing is unique to SGX, but the underlying
concept is the same.

> This how I refactored yesterday (is in my GIT tree already):
> /**
> * sgx_grab_page() - Grab a free EPC page
> * @owner: the owner of the EPC page
> * @reclaim: reclaim pages if necessary
> *
> * Iterate through EPC sections and borrow a free EPC page to the caller. When a
> * page is no longer needed it must be released with sgx_free_page(). If
> * @reclaim is set to true, directly reclaim pages when we are out of pages. No
> * mm's can be locked when @reclaim is set to true.
> *
> * Finally, wake up ksgxswapd when the number of pages goes below the watermark
> * before returning back to the caller.
> *
> * Return:
> * an EPC page,
> * -errno on error
> */
> I also rewrote the kdoc.
> I do agree that sgx_try_grab_page() should be renamed as __sgx_grab_page().

FWIW, I really, really dislike "grab". The nomenclature for normal memory
and pages uses "alloc" when taking a page off a free list, and "grab" when
elevating the refcount. I don't understand the motivation for diverging
from that. SGX is weird enough as is, using names that don't align with
exist norms will only serve to further obfuscate the code.

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