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Subject: Re: [RFC PATCH 3/9] x86/sgx: Allow userspace to add multiple pages in
 single ioctl()
To:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     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>
References: <20190531233159.30992-1-sean.j.christopherson@intel.com>
 <20190531233159.30992-4-sean.j.christopherson@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <beb8ac7a-b580-8ff2-7467-fb2870fb8cf0@intel.com>
Date:   Mon, 3 Jun 2019 13:14:45 -0700
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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.

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? ;)