Messages in this thread | | | Date | Mon, 9 Dec 2019 21:38:22 +0200 | From | Jarkko Sakkinen <> | Subject | Re: [PATCH v24 12/24] x86/sgx: Linux Enclave Driver |
| |
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
| |