linux-kernel - Re: [RFC PATCH v2 4/4] x86/vdso: Add __vdso_sgx_enter_enclave() to wrap SGX enclave transitions

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Message-ID: <20181207203557.GF10404@linux.intel.com>
Date:   Fri, 7 Dec 2018 12:35:57 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Josh Triplett <josh@...htriplett.org>,
        linux-sgx@...r.kernel.org, haitao.huang@...ux.intel.com,
        Jethro Beekman <jethro@...tanix.com>,
        "Dr. Greg Wettstein" <greg@...ellic.com>
Subject: Re: [RFC PATCH v2 4/4] x86/vdso: Add __vdso_sgx_enter_enclave() to
 wrap SGX enclave transitions

On Fri, Dec 07, 2018 at 12:16:59PM -0800, Andy Lutomirski wrote:
> 
> > On Dec 7, 2018, at 12:09 PM, Sean Christopherson <sean.j.christopherson@...el.com> wrote:
> > 
> > Speaking of preserving registers, the asm blob needs to mark RBX as
> > clobbered since it's modified for EEXIT.
> 
> Have fun with that.  The x86_32 compiler seems to really like having its
> PIC register preserved, and you may get some lovely compiler errors.

Tagentinally related, as-is the SGX vDSO is only compiled for x86_64
since CONFIG_SGX depends on CONFIG_X86_64.  Mapping the EPC in 32-bit
mode complicates things and no one is asking for SGX support on 32-bit
builds, so...