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From: Jarkko Sakkinen <jarkko@kernel.org>
To: Haitao Huang <haitao.huang@linux.intel.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	linux-sgx@vger.kernel.org,
	Sean Christopherson <seanjc@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Jethro Beekman <jethro@fortanix.com>
Subject: Re: [PATCH v3] x86/sgx: Synchronize encl->srcu in sgx_encl_release().
Date: Tue, 12 Jan 2021 01:41:27 +0200	[thread overview]
Message-ID: <X/ziJ9a7sRIeNRWr@kernel.org> (raw)
In-Reply-To: <op.0wppi8q8wjvjmi@mqcpg7oapc828.gar.corp.intel.com>

On Mon, Jan 04, 2021 at 02:22:05PM -0600, Haitao Huang wrote:
> On Wed, 16 Dec 2020 07:49:20 -0600, Jarkko Sakkinen <jarkko@kernel.org>
> wrote:
> 
> > Add synchronize_srcu_expedited() to sgx_encl_release() to catch a grace
> > period initiated by sgx_mmu_notifier_release().
> > 
> > A trivial example of a failing sequence with tasks A and B:
> > 
> > 1. A: -> sgx_release()
> > 2. B: -> sgx_mmu_notifier_release()
> > 3. B: -> list_del_rcu()
> > 3. A: -> sgx_encl_release()
> > 4. A: -> cleanup_srcu_struct()
> > 
> > The loop in sgx_release() observes an empty list because B has removed
> > its
> > entry in the middle, and calls cleanup_srcu_struct() before B has a
> > chance
> > to calls synchronize_srcu().
> > 
> > Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Suggested-by: Haitao Huang <haitao.huang@linux.intel.com>
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> > ---
> > v3: Fine-tuned tags, and added missing change log for v2.
> > v2: Switch to synchronize_srcu_expedited().
> >  arch/x86/kernel/cpu/sgx/encl.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/encl.c
> > b/arch/x86/kernel/cpu/sgx/encl.c
> > index ee50a5010277..fe7256db6e73 100644
> > --- a/arch/x86/kernel/cpu/sgx/encl.c
> > +++ b/arch/x86/kernel/cpu/sgx/encl.c
> > @@ -438,6 +438,12 @@ void sgx_encl_release(struct kref *ref)
> >  	if (encl->backing)
> >  		fput(encl->backing);
> > +	/*
> > +	 * Each sgx_mmu_notifier_release() starts a grace period. Therefore, an
> > +	 * additional sync is required here.
> > +	 */
> > +	synchronize_srcu_expedited(&encl->srcu);
> > +
> >  	cleanup_srcu_struct(&encl->srcu);
> > 	WARN_ON_ONCE(!list_empty(&encl->mm_list));
> 
> Tested-by: Haitao Huang <haitao.huang@linux.intel.com>

Thanks.

/Jarkko

  reply	other threads:[~2021-01-12  0:27 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-16 13:49 [PATCH v3] x86/sgx: Synchronize encl->srcu in sgx_encl_release() Jarkko Sakkinen
2021-01-04 20:22 ` Haitao Huang
2021-01-11 23:41   ` Jarkko Sakkinen [this message]
2021-01-05 14:57 ` Borislav Petkov
2021-01-12  0:08   ` Jarkko Sakkinen
2021-01-12 18:35     ` Borislav Petkov
2021-01-12 20:11       ` Paul E. McKenney
2021-01-13 17:18       ` Jarkko Sakkinen
2021-01-13 17:46         ` Paul E. McKenney
2021-01-13 18:00           ` Borislav Petkov
2021-01-13 18:22             ` Paul E. McKenney
2021-01-15  1:49           ` Jarkko Sakkinen
2021-01-14  4:42     ` Haitao Huang
2021-01-15  9:58       ` Jarkko Sakkinen

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