linux-kernel - Re: [PATCH] lib: Add test module for CONFIG_DEBUG

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Date:   Tue, 8 Aug 2017 11:04:11 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, ard.biesheuvel@...aro.org,
        labbott@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Olof Johansson <olof@...om.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Theodore Ts'o <tytso@....edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jiri Pirko <jiri@...lanox.com>,
        Jeff Layton <jlayton@...hat.com>
Subject: Re: [PATCH] lib: Add test module for CONFIG_DEBUG_VIRTUAL

On 08/08/2017 10:57 AM, Luis R. Rodriguez wrote:
> On Tue, Aug 08, 2017 at 09:40:26AM -0700, Florian Fainelli wrote:
>> Add a test module that allows testing that CONFIG_DEBUG_VIRTUAL works
>> correctly, at least that it can catch invalid calls to virt_to_phys()
>> against the non-linear kernel virtual address map.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>> ---

>> +static int __init test_debug_virtual_init(void)
>> +{
>> +	phys_addr_t pa;
>> +	void *va;
>> +
>> +	va = (void *)VMALLOC_START;
>> +	pa = virt_to_phys(va);
>> +
>> +	pr_info("PA: %pa for VA: 0x%lx\n", &pa, (unsigned long)va);
>> +
>> +	foo = kzalloc(sizeof(*foo), GFP_KERNEL);
>> +	if (!foo)
>> +		return -ENOMEM;
>> +
>> +	pa = virt_to_phys(foo);
>> +	va = foo;
>> +	pr_info("PA: %pa for VA: 0x%lx\n", &pa, (unsigned long)va);
> 
> Should there be a tests here of some sort? When should this fail, why?

There is no test per-se, the kernel will produce warning with
CONFIG_DEBUG_VIRTUAL telling you that what you are doing is wrong.

> There is no docs on this self test, could one be added?

I suppose I could add one even though that just means pointing out the
code that produces the warning?
-- 
Florian