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Date:   Mon, 3 Jun 2019 13:37:12 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Cedric Xing <cedric.xing@intel.com>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        James Morris <jmorris@namei.org>,
        "Serge E . Hallyn" <serge@hallyn.com>,
        LSM List <linux-security-module@vger.kernel.org>,
        Paul Moore <paul@paul-moore.com>,
        Eric Paris <eparis@parisplace.org>, selinux@vger.kernel.org,
        Jethro Beekman <jethro@fortanix.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        linux-sgx@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>, nhorman@redhat.com,
        npmccallum@redhat.com, Serge Ayoun <serge.ayoun@intel.com>,
        Shay Katz-zamir <shay.katz-zamir@intel.com>,
        Haitao Huang <haitao.huang@intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Kai Svahn <kai.svahn@intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Josh Triplett <josh@joshtriplett.org>,
        Kai Huang <kai.huang@intel.com>,
        David Rientjes <rientjes@google.com>,
        William Roberts <william.c.roberts@intel.com>,
        Philip Tricca <philip.b.tricca@intel.com>
Subject: Re: [RFC PATCH 3/9] x86/sgx: Allow userspace to add multiple pages
 in single ioctl()
Message-ID: <20190603203712.GI13384@linux.intel.com>
References: <20190531233159.30992-1-sean.j.christopherson@intel.com>
 <20190531233159.30992-4-sean.j.christopherson@intel.com>
 <beb8ac7a-b580-8ff2-7467-fb2870fb8cf0@intel.com>
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On Mon, Jun 03, 2019 at 01:14:45PM -0700, Dave Hansen wrote:
> On 5/31/19 4:31 PM, Sean Christopherson wrote:
> > -struct sgx_enclave_add_page {
> > +struct sgx_enclave_add_pages {
> >  	__u64	addr;
> >  	__u64	src;
> >  	__u64	secinfo;
> > +	__u32	nr_pages;
> >  	__u16	mrmask;
> >  } __attribute__((__packed__));
> 
> IMNHO this follows a user interface anti-pattern: exposing page sizes
> where not strictly required.
> 
> Think of how this would look to an application if page size was
> variable.  With this interface, they always need to scale their
> operations by page size instead of just aligning it.

I briefly considered taking size in bytes, but I took a shortcut because
EPC pages are architecturally defined to be 4k sized and aligned.  That
being said, I don't necessarily disagree, especially if nr_pages isn't
squeezed into a u32.
 
> BTW, why is nr_pages a u32?  Do we never envision a case where you can
> add more than 4TB of memory to an enclave? ;)

Heh, fair enough.  IIRC, a while back someone posted about having problems
building a 512gb enclave in a 92mb EPC...

How about this for the intermediate patch:

	struct sgx_enclave_add_region {
		__u64	addr;
		__u64	src;
		__u64	size;
		__u64	secinfo;
		__u16	mrmask;
		__u16	reserved16;
		__u32	reserved;
	}

and with the flags field:

	struct sgx_enclave_add_region {
		__u64	addr;
		__u64	src;
		__u64	size;
		__u64	secinfo;
		__u16	mrmask;
		__u16	flags;
		__u32	reserved;
	}