linux-kernel - Re: [PATCH] x86/sgx: fix a NULL pointer

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Date:   Tue, 18 Jul 2023 16:57:08 -0500
From:   "Haitao Huang" <haitao.huang@...ux.intel.com>
To:     "Jarkko Sakkinen" <jarkko@...nel.org>, dave.hansen@...ux.intel.com,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        "Dave Hansen" <dave.hansen@...el.com>
Cc:     kai.huang@...el.com, reinette.chatre@...el.com,
        kristen@...ux.intel.com, seanjc@...gle.com, stable@...r.kernel.org
Subject: Re: [PATCH] x86/sgx: fix a NULL pointer

On Tue, 18 Jul 2023 16:36:53 -0500, Dave Hansen <dave.hansen@...el.com>  
wrote:

> On 7/18/23 14:22, Haitao Huang wrote:
>> I agree this is the race. But for this to happen, that is at #1 you have
>> only one non-SECS page left so #3 can happen. That means it is already
>> high pressure
>
> I think our definitions of memory pressure differ.
>
> Pressure is raised by allocations and dropped by reclaim.  This
> raise->drop cycle is (or should be) time-limited and can't take forever.
>  The reclaim either works in a short period of time or something dies.
> If allocations are transient, pressure is transient.
>
> Let's say a pressure blip (a one-time event) comes along and pages out
> that second-to-last page.  That's pretty low pressure.  Years pass.  The
> enclave never gets run.  Nothing pages the second-to-last page back in.
> A second pressure blip comes along.  The SECS page gets paged out.
>
> That's two pressure blips in, say 10 years.  Is that "high pressure"?

Okay, that explains. I would consider it still triggered by high pressure  
blips :-)

But I agree we can drop the mentioning of pressure altogether and just  
state the race so no confusions.
Thanks
Haitao