linux-kernel - Re: [PATCH] x86/sgx: Synchronize encl->srcu in sgx_encl

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Message-ID: <20201215055955.GA28511@kernel.org>
Date:   Tue, 15 Dec 2020 07:59:55 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-sgx@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH] x86/sgx: Synchronize encl->srcu in sgx_encl_release().

On Tue, Dec 15, 2020 at 07:56:01AM +0200, Jarkko Sakkinen wrote:
> On Mon, Dec 14, 2020 at 11:01:32AM -0800, Sean Christopherson wrote:
> > On Fri, Dec 11, 2020, Jarkko Sakkinen wrote:
> > > Each sgx_mmun_notifier_release() starts a grace period, which means that
> > 
> > Should be sgx_mmu_notifier_release(), here and in the comment.
> 
> Thanks.
> 
> > > one extra synchronize_rcu() in sgx_encl_release(). Add it there.
> > > 
> > > sgx_release() has the loop that drains the list but with bad luck the
> > > entry is already gone from the list before that loop processes it.
> > 
> > Why not include the actual analysis that "proves" the bug?  The splat that
> > Haitao reported would also be useful info.
> 
> True. I can include a snippet of dmesg to the commit message.
> 
> > > Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
> > > Cc: Borislav Petkov <bp@...en8.de>
> > > Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> > > Reported-by: Sean Christopherson <seanjc@...gle.com>
> > 
> > Haitao reported the bug, and for all intents and purposes provided the fix.  I
> > just did the analysis to verify that there was a legitimate bug and that the
> > synchronization in sgx_encl_release() was indeed necessary.
> 
> Good and valid point. The way I see it, the tags should be:
> 
> Reported-by: Haitao Huang <haitao.huang@...ux.intel.com>
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> 
> Haitao pointed out the bug but from your analysis I could resolve that
> this is the fix to implement, and was able to write the long
> description for the commit.
> 
> Does this make sense to you?

I'm sending v2 next week (this week on vacation).

/Jarkko