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

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Message-ID: <YeIN1RQydD1juJGA@iki.fi>
Date:   Sat, 15 Jan 2022 01:57:09 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        linux-sgx@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] x86/sgx: account backing pages

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