From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.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 07:44:49 -0700 [thread overview]
Message-ID: <20200406144449.GD21330@linux.intel.com> (raw)
In-Reply-To: <20200406143155.GA21330@linux.intel.com>
On Mon, Apr 06, 2020 at 07:31:55AM -0700, Sean Christopherson wrote:
> On Sat, Apr 04, 2020 at 04:12:48AM +0300, Jarkko Sakkinen wrote:
> > On Fri, Apr 03, 2020 at 04:35:47PM -0700, Sean Christopherson wrote:
> > > On Sat, Apr 04, 2020 at 02:33:31AM +0300, Jarkko Sakkinen wrote:
> > > > On Fri, Apr 03, 2020 at 12:35:50PM +0300, Jarkko Sakkinen wrote:
> > > > > From: Sean Christopherson <sean.j.christopherson@intel.com>
> > > > > - idx = srcu_read_lock(&encl->srcu);
> > > > > + do {
> > > > > + mm_list_version = encl->mm_list_version;
> > > > >
> > > > > - list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
> > > > > - if (!mmget_not_zero(encl_mm->mm))
> > > > > - continue;
> > > > > + /* Fence reads as the CPU can reorder them. This guarantees
> > > > > + * that we don't access old list with a new version.
> > > > > + */
> > > > > + smp_rmb();
> > > > >
> > > > > - down_read(&encl_mm->mm->mmap_sem);
> > > > > + idx = srcu_read_lock(&encl->srcu);
> > > > >
> > > > > - ret = sgx_encl_find(encl_mm->mm, addr, &vma);
> > > > > - if (!ret && encl == vma->vm_private_data)
> > > > > - zap_vma_ptes(vma, addr, PAGE_SIZE);
> > > > > + list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
> > > > > + if (!mmget_not_zero(encl_mm->mm))
> > > > > + continue;
> > > > >
> > > > > - up_read(&encl_mm->mm->mmap_sem);
> > > > > + down_read(&encl_mm->mm->mmap_sem);
> > > > >
> > > > > - mmput_async(encl_mm->mm);
> > > > > - }
> > > > > + ret = sgx_encl_find(encl_mm->mm, addr, &vma);
> > > > > + if (!ret && encl == vma->vm_private_data)
> > > > > + zap_vma_ptes(vma, addr, PAGE_SIZE);
> > > > >
> > > > > - srcu_read_unlock(&encl->srcu, idx);
> > > > > + up_read(&encl_mm->mm->mmap_sem);
> > > > > +
> > > > > + mmput_async(encl_mm->mm);
> > > > > + }
> > > > > +
> > > > > + srcu_read_unlock(&encl->srcu, idx);
> > > > > + } while (unlikely(encl->mm_list_version != mm_list_version));
> > > >
> > > > This is bad, or at least makes the code unnecessarily hard to understand
> > > > given the use of the fences: encl->mm_list_version is read twice per
> > > > iteration.
> > > >
> > > > I'll change the code to use "for ( ; ; )" and have exactly one read per
> > > > iteration.
> > >
> > > It has to be read twice per iteration, the whole point is to see if the
> > > version at the start of the iteration matches the version at the end.
> >
> > Nope if you use zero version as invalid version.
>
> Which would break if more than one mm is added to an enclave.
Ah, you mean within the function (just saw v3).
next prev parent reply other threads:[~2020-04-06 14:44 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 [this message]
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
2020-04-09 19:13 ` Sean Christopherson
2020-04-10 13:22 ` Jarkko Sakkinen
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