Re: [PATCH] x86/sgx: Synchronize encl->srcu in sgx_encl_release().

[Haitao Huang]

On Mon, 14 Dec 2020 23:59:55 -0600, Jarkko Sakkinen <jarkko@xxxxxxxxxx>
wrote:

> 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@xxxxxxxxx>
> > > > Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> > > > Reported-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxxxxxxx>
> > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> >
> > 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

I don't mind either how tags are assigned. But our testing reveals
significant latency introduced in scenarios of heavy loading/unloading
enclaves. synchronize_srcu_expedited fixed the issue. Please analyze and
confirm if that's more appropriate than synchronize_srcu here.