From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: linux-sgx@vger.kernel.org, Haitao Huang <haitao.huang@linux.intel.com>
Subject: Re: [PATCH v2] x86/sgx: Fix deadlock and race conditions between fork() and EPC reclaim
Date: Mon, 6 Apr 2020 20:15:56 +0300 [thread overview]
Message-ID: <20200406171556.GB20105@linux.intel.com> (raw)
In-Reply-To: <20200406171027.GA20105@linux.intel.com>
On Mon, Apr 06, 2020 at 08:10:29PM +0300, Jarkko Sakkinen wrote:
> On Mon, Apr 06, 2020 at 07:36:38AM -0700, Sean Christopherson wrote:
> > On Sat, Apr 04, 2020 at 04:12:02AM +0300, Jarkko Sakkinen wrote:
> > > On Fri, Apr 03, 2020 at 04:42:39PM -0700, Sean Christopherson wrote:
> > > > On Fri, Apr 03, 2020 at 12:35:50PM +0300, Jarkko Sakkinen wrote:
> > > > > From: Sean Christopherson <sean.j.christopherson@intel.com>
> > > > > @@ -221,12 +224,16 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm)
> > > > > return ret;
> > > > > }
> > > > >
> > > > > + /*
> > > > > + * The page reclaimer uses list version for synchronization instead of
> > > > > + * synchronize_scru() because otherwise we could conflict with
> > > > > + * dup_mmap().
> > > > > + */
> > > > > spin_lock(&encl->mm_lock);
> > > > > list_add_rcu(&encl_mm->list, &encl->mm_list);
> > > >
> > > > You dropped the smp_wmb().
> > >
> > > As I said to you in my review x86 pipeline does not reorder writes.
> >
> > And as I pointed out in this thread, smp_wmb() is a _compiler_ barrier if
> > and only if CONFIG_SMP=y. The compiler can reorder list_add_rcu() and
> > mm_list_version++ because from it's perspective there is no dependency
> > between the two. And that's entirely true except for the SMP case where
> > the consumer of mm_list_version is relying on the list to be updated before
> > the version changes.
>
> I see.
>
> So why not change the variable volatile given that x86 is the only
> arch that this code gets used?
Please note that I'm fully aware of
https://www.kernel.org/doc/html/latest/process/volatile-considered-harmful.html
Just wondering. Anyway, I'll add smp_wmb() back since it is safe play
in terms of acceptance.
/Jarkko
next prev parent reply other threads:[~2020-04-06 17:16 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-03 9:35 [PATCH v2] x86/sgx: Fix deadlock and race conditions between fork() and EPC reclaim Jarkko Sakkinen
2020-04-03 23:33 ` Jarkko Sakkinen
2020-04-03 23:35 ` Sean Christopherson
2020-04-04 1:12 ` Jarkko Sakkinen
2020-04-06 14:31 ` Sean Christopherson
2020-04-06 14:44 ` Sean Christopherson
2020-04-03 23:42 ` Sean Christopherson
2020-04-04 1:12 ` Jarkko Sakkinen
2020-04-06 14:36 ` Sean Christopherson
2020-04-06 17:10 ` Jarkko Sakkinen
2020-04-06 17:15 ` Jarkko Sakkinen [this message]
2020-04-09 19:13 ` Sean Christopherson
2020-04-10 13:22 ` Jarkko Sakkinen
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