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From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Haitao Huang <haitao.huang@linux.intel.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	linux-sgx@vger.kernel.org, akpm@linux-foundation.org,
	dave.hansen@intel.com, nhorman@redhat.com, npmccallum@redhat.com,
	serge.ayoun@intel.com, shay.katz-zamir@intel.com,
	haitao.huang@intel.com, andriy.shevchenko@linux.intel.com,
	tglx@linutronix.de, kai.svahn@intel.com, bp@alien8.de,
	josh@joshtriplett.org, luto@kernel.org, kai.huang@intel.com,
	rientjes@google.com, cedric.xing@intel.com,
	puiterwijk@redhat.com, linux-security-module@vger.kernel.org,
	Suresh Siddha <suresh.b.siddha@intel.com>
Subject: Re: [PATCH v24 12/24] x86/sgx: Linux Enclave Driver
Date: Mon, 9 Dec 2019 21:38:22 +0200
Message-ID: <20191209193822.GB19243@linux.intel.com> (raw)
In-Reply-To: <20191202182102.GF4063@linux.intel.com>

On Mon, Dec 02, 2019 at 10:21:03AM -0800, Sean Christopherson wrote:
> On Mon, Dec 02, 2019 at 09:48:43AM -0600, Haitao Huang wrote:
> > On Fri, 29 Nov 2019 17:13:14 -0600, Jarkko Sakkinen
> > <jarkko.sakkinen@linux.intel.com> wrote:
> > 
> > 
> > >+
> > >+	for (c = 0 ; c < addp.length; c += PAGE_SIZE) {
> > >+		if (signal_pending(current)) {
> > >+			ret = -ERESTARTSYS;
> > >+			break;
> > >+		}
> > 
> > This IOC is not idempotent as pages EADDed at this point can not be
> > re-EADDed again. So we can't return ERESTARTSYS
> 
> Ah, and now I remember why I opted for modifying the parameters directly
> instead of including a "number processed" field.  Andy pointed out the
> ERESTARTSYS thing in the original multi-page add RFC[*], so presumably
> updating the params and returning ERESTARTSYS is legal/acceptable.
> 
> [*] https://lkml.kernel.org/r/CALCETrUb4X9_L9RXKhmyNpfSCsbNodP=BfbfO8Fz_efq24jp8w@mail.gmail.com

There are exactly two primary options to pick from given the
non-idempotent nature:

A. Return zero (since we support partial operation with the changes I
   did in v24).
B. Return -EINTR.

If we wanted to follow common syscall semantics in IO operations, then
the semantics would be a mix of these:

1. Return -EINTR if signals are pending before any pages got added.
2. Return 0 if at least one page got added.

This is how write() works for example according to the documentation
[1]. As far as the user code goes [2] I think for that it is best
idea to rely on semantics that developers are used to instead of
being clever here.

[1] http://man7.org/linux/man-pages/man2/write.2.html
[2] https://lkml.kernel.org/r/CALCETrUb4X9_L9RXKhmyNpfSCsbNodP=BfbfO8Fz_efq24jp8w@mail.gmail.com

/Jarkko

  reply index

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-29 23:13 [PATCH v24 00/24] Intel SGX foundations Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 01/24] x86/sgx: Update MAINTAINERS Jarkko Sakkinen
2019-11-30  1:38   ` Neil Horman
2019-11-30 14:37     ` Dr. Greg
2019-12-02  9:24       ` Jethro Beekman
2019-12-06 21:23     ` Jarkko Sakkinen
2019-12-06 21:24       ` Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 02/24] x86/cpufeatures: x86/msr: Add Intel SGX hardware bits Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 03/24] x86/cpufeatures: x86/msr: Intel SGX Launch Control " Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 04/24] x86/mm: x86/sgx: Signal SIGSEGV with PF_SGX Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 05/24] x86/sgx: Add SGX microarchitectural data structures Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 06/24] x86/sgx: Add wrappers for ENCLS leaf functions Jarkko Sakkinen
2019-12-17 14:45   ` Borislav Petkov
2019-12-19  0:39     ` Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 07/24] x86/cpu/intel: Detect SGX supprt Jarkko Sakkinen
2019-12-17 15:17   ` Borislav Petkov
2019-12-19  0:42     ` Jarkko Sakkinen
2019-12-19  6:15       ` Borislav Petkov
2019-12-23  9:46   ` Borislav Petkov
2019-12-27  6:00     ` Jarkko Sakkinen
2020-01-14 18:36     ` Sean Christopherson
2019-11-29 23:13 ` [PATCH v24 08/24] x86/sgx: Enumerate and track EPC sections Jarkko Sakkinen
2019-12-18  9:18   ` Borislav Petkov
2019-12-18 15:19     ` Sean Christopherson
2019-12-18 16:18       ` Borislav Petkov
2019-12-19  0:53     ` Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 09/24] x86/sgx: Add functions to allocate and free EPC pages Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 10/24] x86/sgx: Add sgx_einit() for wrapping ENCLS[EINIT] Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 11/24] mm: Introduce vm_ops->may_mprotect() Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 12/24] x86/sgx: Linux Enclave Driver Jarkko Sakkinen
2019-12-02 15:48   ` Haitao Huang
2019-12-02 18:21     ` Sean Christopherson
2019-12-09 19:38       ` Jarkko Sakkinen [this message]
2019-12-09 19:08     ` Jarkko Sakkinen
2020-01-14 16:12   ` Haitao Huang
2019-11-29 23:13 ` [PATCH v24 13/24] selftests/x86: Recurse into subdirectories Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 14/24] selftests/x86: Add a selftest for SGX Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 15/24] x86/sgx: Add provisioning Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 16/24] x86/sgx: Add a page reclaimer Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 17/24] x86/sgx: ptrace() support for the SGX driver Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 18/24] x86/vdso: Add support for exception fixup in vDSO functions Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 19/24] x86/fault: Add helper function to sanitize error code Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 20/24] x86/traps: Attempt to fixup exceptions in vDSO before signaling Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 21/24] x86/vdso: Add __vdso_sgx_enter_enclave() to wrap SGX enclave transitions Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 22/24] selftests/x86: Add vDSO selftest for SGX Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 23/24] docs: x86/sgx: Document microarchitecture Jarkko Sakkinen
2019-11-29 23:13 ` [PATCH v24 24/24] docs: x86/sgx: Document kernel internals Jarkko Sakkinen
2019-12-20 13:26 ` [PATCH v24 00/24] Intel SGX foundations Nathaniel McCallum

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