From: Dave Hansen <dave.hansen@intel.com>
To: Jethro Beekman <jethro@fortanix.com>,
Raoul Strackx <raoul.strackx@fortanix.com>,
Jarkko Sakkinen <jarkko@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RESEND 0/3] x86/sgx: eextend ioctl
Date: Fri, 2 Apr 2021 11:42:53 -0700 [thread overview]
Message-ID: <5af533e2-5bfd-8edc-0eaa-6fd3ddebb211@intel.com> (raw)
In-Reply-To: <9a841584-65e8-31e9-6bd4-0140b33434e8@fortanix.com>
On 4/2/21 11:31 AM, Jethro Beekman wrote:
> On 2021-04-02 17:53, Dave Hansen wrote:
>> On 4/2/21 1:38 AM, Jethro Beekman wrote:
>>>> So, we're talking here about pages that have been EEADDED, but for
>>>> which we do not want to include the entire contents of the page?
>>>> Do these contents always include the beginning of the page, or can
>>>> the holes be anywhere?
>>> Holes can be anywhere, and EEXTEND calls need not be sequential in
>>> memory address or even relate to the most recently EADDed page.
>>
>> I think you're referring to the SGX architecture itself here. The
>> architecture permits this, right?
>
> Yes.
>
>> But, why would an enclave loader application ever do this?
>
> e.g. to save space
How does this save space, exactly? What space does it save?
Let's say I want to add 4352 bytes of data to an enclave. Today, I have
to page-align the beginning and end of that 4352 bytes, and call the add
ioctl() to add the two resulting pages. It consumes two EPC pages.
With EEXTEND, if I want to add the data, I only need to page-align the
beginning of the data. I call add_page on the first page, then eextend
on the 256 bytes. It consumes two EPC pages.
I guess you can argue that this saves padding out the second page, which
would *theoretically* temporarily eat up one extra page of non-enclave
memory and the cost of a 256-byte memcpy.
>> Is this something we want to support in Linux?
>
> Why not? Is there a good reason to not fully support this part of the
> CPU architecture?
We don't blindly support CPU features in Linux. They need to do
something *useful*. I'm still missing what this does which is useful.
Does any actual, real-world enclave want this functionality? Why?
P.S. There are plenty of things you can do with the SGX architecture
that we probably won't ever implement in Linux.
next prev parent reply other threads:[~2021-04-02 18:42 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-31 12:50 [PATCH RESEND 0/3] x86/sgx: eextend ioctl Raoul Strackx
2021-03-31 15:53 ` Dave Hansen
2021-04-01 14:56 ` Raoul Strackx
2021-04-01 16:11 ` Dave Hansen
2021-04-01 17:49 ` Raoul Strackx
2021-04-01 18:40 ` Dave Hansen
2021-04-02 8:38 ` Jethro Beekman
2021-04-02 15:53 ` Dave Hansen
2021-04-02 18:31 ` Jethro Beekman
2021-04-02 18:42 ` Dave Hansen [this message]
2021-04-02 19:38 ` Jethro Beekman
2021-04-02 19:50 ` Dave Hansen
2021-04-02 20:20 ` Jethro Beekman
2021-04-02 20:48 ` Dave Hansen
2021-04-08 15:27 ` Jethro Beekman
2021-04-08 15:54 ` Dave Hansen
2021-04-04 16:04 ` Jarkko Sakkinen
2021-04-08 15:07 ` Jethro Beekman
2021-04-01 17:59 ` Jethro Beekman
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