linux-kernel - Re: [PATCH V8 19/44] mm/pkeys: PKS Testing, add pks_mk

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Date:   Tue, 1 Feb 2022 09:45:03 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     ira.weiny@...el.com, Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V8 19/44] mm/pkeys: PKS Testing, add pks_mk_*() tests

On 1/27/22 09:54, ira.weiny@...el.com wrote:
>  bool pks_test_callback(void)
>  {
> -	return false;
> +	bool armed = (test_armed_key != 0);
> +
> +	if (armed) {
> +		pks_mk_readwrite(test_armed_key);
> +		fault_cnt++;
> +	}
> +
> +	return armed;
> +}

Where's the locking for all this?  I don't think we need anything fancy,
but is there anything preventing the test from being started from
multiple threads at the same time?  I think a simple global test mutex
would probably suffice.

Also, pks_test_callback() needs at least a comment or two about what
it's doing.

Does this work if you have a test armed and then you get an unrelated
PKS fault on another CPU?  I think this will disarm the test from the
unrelated thread.