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Date:   Fri, 13 Mar 2020 09:33:26 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Nathaniel McCallum <npmccallum@redhat.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        linux-sgx@vger.kernel.org, akpm@linux-foundation.org,
        dave.hansen@intel.com, Neil Horman <nhorman@redhat.com>,
        "Huang, Haitao" <haitao.huang@intel.com>,
        andriy.shevchenko@linux.intel.com, tglx@linutronix.de,
        "Svahn, Kai" <kai.svahn@intel.com>, bp@alien8.de,
        Josh Triplett <josh@joshtriplett.org>, luto@kernel.org,
        kai.huang@intel.com, David Rientjes <rientjes@google.com>,
        cedric.xing@intel.com, Patrick Uiterwijk <puiterwijk@redhat.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Jethro Beekman <jethro@fortanix.com>
Subject: Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX
 enclave call
Message-ID: <20200313163326.GB5181@linux.intel.com>
References: <20200303233609.713348-1-jarkko.sakkinen@linux.intel.com>
 <20200303233609.713348-22-jarkko.sakkinen@linux.intel.com>
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On Fri, Mar 13, 2020 at 12:07:55PM -0400, Nathaniel McCallum wrote:
> On Thu, Mar 12, 2020 at 8:52 PM Sean Christopherson
> <sean.j.christopherson@intel.com> wrote:
> > FWIW, if the handler reaaaly wanted to pop off the stack, it could do so,
> > fixup the stack, and then re-call __vdso_sgx_enter_enclave() instead of
> > returning (to the original __vdso_sgx_enter_enclave()).
> 
> My understanding from the documentation issue above was that *if* you
> wanted to push parameters back on the stack during enclave exit, you
> would *have* to supply a handler so it could pop the parameters and
> reset the stack. Which is why restoring %rsp from %rbx didn't make
> sense to me.

Yep.