linux-kernel - Re: [PATCH] x86/sgx: Fix free page accounting

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Date:   Sun, 07 Nov 2021 18:47:58 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Reinette Chatre <reinette.chatre@...el.com>,
        dave.hansen@...ux.intel.com, tglx@...utronix.de, bp@...en8.de,
        mingo@...hat.com, linux-sgx@...r.kernel.org, x86@...nel.org
Cc:     seanjc@...gle.com, tony.luck@...el.com, hpa@...or.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/sgx: Fix free page accounting

On Sun, 2021-11-07 at 18:45 +0200, Jarkko Sakkinen wrote:
> On Thu, 2021-11-04 at 11:28 -0700, Reinette Chatre wrote:
> > The consequence of sgx_nr_free_pages not being protected is that
> > its value may not accurately reflect the actual number of free
> > pages on the system, impacting the availability of free pages in
> > support of many flows. The problematic scenario is when the
> > reclaimer never runs because it believes there to be sufficient
> > free pages while any attempt to allocate a page fails because there
> > are no free pages available. The worst scenario observed was a
> > user space hang because of repeated page faults caused by
> > no free pages ever made available.
> 
> Can you go in detail with the "concrete scenario" in the commit
> message? It does not have to describe all the possible scenarios
> but at least one sequence of events.

I.e. I don't have anything fundamentally against changing it to
atomic but the commit message is completely lacking the stimulus
of changing anything.

/Jarkko