linux-kernel - Re: [RFC PATCH v5 0/5] x86: Add vDSO exception fixup for SGX

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Date:   Tue, 18 Dec 2018 07:08:15 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        linux-sgx@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
        Josh Triplett <josh@...htriplett.org>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Jethro Beekman <jethro@...tanix.com>,
        "Dr . Greg Wettstein" <greg@...ellic.com>
Subject: Re: [RFC PATCH v5 0/5] x86: Add vDSO exception fixup for SGX

On Tue, Dec 18, 2018 at 06:18:15AM +0200, Jarkko Sakkinen wrote:
> On Fri, Dec 14, 2018 at 01:57:24PM -0800, Sean Christopherson wrote:
> > __vdso_sgx_enter_enclave() gets another rewrite, this time to strip
> > it down to the bare minimum and explicitly break compliance with the
> > x86-64 ABI.  Feedback from v4 revealed that __vdso_sgx_enter_enclave()
> > would need to save (a lot) more than just the non-volatile GPRs to be
> > compliant with the x86-64 ABI, at which point breaking from the ABI
> > completely became much more palatable.
> > 
> > The non-standard ABI also solves the question of "which GPRs should be
> > marshalled to/from the enclave" by getting out of the way entirely and
> > letting userspace have free reign (except for RSP, which has a big ol'
> > DO NOT TOUCH sign on it).
> 
> Can you share a reference, or is this better documented in the
> accompanied patches?

Patch 5/5 has more details, and v4 of the series has a lot of background
info by way of discussion:

https://lkml.kernel.org/r/20181213213135.12913-1-sean.j.christopherson@intel.com