linux-kernel - Re: [PATCH v6 06/11] intel_sgx: driver for Intel Software Guard Extensions

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Message-ID: <20171126184627.hegr3qzgous5ivpe@linux.intel.com>
Date:   Sun, 26 Nov 2017 20:46:27 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     platform-driver-x86@...r.kernel.org, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>
Subject: Re: [PATCH v6 06/11] intel_sgx: driver for Intel Software Guard
 Extensions

On Sun, Nov 26, 2017 at 07:33:56PM +0200, Jarkko Sakkinen wrote:
> > +struct sgx_encl_page {
> > +	unsigned long addr;
> > +	unsigned int flags;
> > +	void *epc_page;
> > +	struct sgx_va_page *va_page;
> > +	unsigned int va_offset;
> > +	struct list_head list;
> > +};
> 
> This can be without major streches hoops packed way more. There are 12
> bits free for use in the addr field. I can use low three bits for flags
> and upper nine bits for va_offset.
> 
> I think I can also quite easily union epc_page and va_page fields.
> 
> With these changes the struct would shrink to:
> 
> struct sgx_encl_page {
> 	unsigned long addr;
> 	union {
> 		void *epc_page;
> 		struct sgx_va_page *va_page;
> 	};
> 	struct list_head list;
> };

Once I started to thinking more about this I realized that this can be
shrunk even further. I can drop the list field and use a tag for loaded
pages in the radix tree where these are stored. The end result would be

struct sgx_encl_page {
	unsigned long addr;
 	union {
 		void *epc_page;
 		struct sgx_va_page *va_page;
 	};
};

/Jarkko