Re: [PATCH 4/7] x86/sgx: Allow userspace to add multiple pages in single ioctl()

From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Jethro Beekman <jethro@fortanix.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	"linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Cedric Xing <cedric.xing@intel.com>,
	"Dr . Greg Wettstein" <greg@enjellic.com>
Subject: Re: [PATCH 4/7] x86/sgx: Allow userspace to add multiple pages in single ioctl()
Date: Thu, 13 Jun 2019 12:15:59 -0700	[thread overview]
Message-ID: <20190613191559.GA18385@linux.intel.com> (raw)
In-Reply-To: <CALCETrU8ZNL==n+fC2aH7437cstq68Xu8LJnQFnOFGCWc1L3OQ@mail.gmail.com>

On Thu, Jun 13, 2019 at 12:05:37PM -0700, Andy Lutomirski wrote:
> On Thu, Jun 13, 2019 at 9:51 AM Sean Christopherson
> <sean.j.christopherson@intel.com> wrote:
> > If we ditch the workqueue then we probably don't even need to gift the
> > page, e.g. I think we allocate the EPC page prior to taking mmap_sem, and
> > then simply do gup+kmap around EADD.  We'd just need to be careful about
> > not allocating EPC pages for ioctls that are guaranteed to fail.
> >
> >
> 
> Why gup + kmap?  Can't you just do STAC; EADD; CLAC?  (Using the
> appropriate C helpers, of course.)

That should work as well, we already have exception fixup on ENCLS.  I
obviously haven't given much thought to what all we can do once the
workqueue goes bye bye :-)