linux-kernel - Re: [PATCH v30 08/20] x86/sgx: Add functions to allocate and free EPC pages

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Date:   Thu, 28 May 2020 12:59:17 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-sgx@...r.kernel.org,
        akpm@...ux-foundation.org, dave.hansen@...el.com,
        nhorman@...hat.com, npmccallum@...hat.com, haitao.huang@...el.com,
        andriy.shevchenko@...ux.intel.com, tglx@...utronix.de,
        kai.svahn@...el.com, josh@...htriplett.org, luto@...nel.org,
        kai.huang@...el.com, rientjes@...gle.com, cedric.xing@...el.com,
        puiterwijk@...hat.com, Jethro Beekman <jethro@...tanix.com>
Subject: Re: [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.