linux-kernel - Re: [PATCH] livepatch: Cleanup page permission changes

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Message-ID: <alpine.LNX.2.00.1511051019460.22567@pobox.suse.cz>
Date:	Thu, 5 Nov 2015 10:28:13 +0100 (CET)
From:	Jiri Kosina <jikos@...nel.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
cc:	Miroslav Benes <mbenes@...e.cz>,
	Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.com>,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	"Cyril B." <cbay@...aysdata.com>
Subject: Re: [PATCH] livepatch: Cleanup page permission changes

On Wed, 4 Nov 2015, Josh Poimboeuf wrote:

> > >  int klp_write_module_reloc(struct module *mod, unsigned long type,
> > >  			   unsigned long loc, unsigned long value)
> > >  {
> > > -	int ret, numpages, size = 4;
> > > -	bool readonly;
> > > +	int size = 4;
> > 
> > BTW I don't see a reason to have 'size' signed here.
> 
> It was already signed to begin with, but I can change it to size_t.

Yes, I know, it's not really related to this patchset, but I stumbled upon 
it during review.

> > > +#ifdef CONFIG_DEBUG_SET_MODULE_RONX
> > > +static void set_page_attributes(void *start, void *end,
> > > +				int (*set)(unsigned long start, int num_pages))
> > > +{
> > > +	unsigned long begin_pfn = PFN_DOWN((unsigned long)start);
> > > +	unsigned long end_pfn = PFN_DOWN((unsigned long)end);
> > > +
> > > +	if (end_pfn > begin_pfn)
> > > +		set(begin_pfn << PAGE_SHIFT, end_pfn - begin_pfn);
> > > +}

BTW is there any reason not to make use of the function from module.c 
which does exactly the same, instead of copy pasting it all around?

> > > +static void set_module_ro_rw(struct module *mod)
> > > +{
> > > +	set_page_attributes(mod->module_core,
> > > +			    mod->module_core + mod->core_ro_size,
> > > +			    set_memory_rw);
> > > +}
> > > +static void set_module_ro_ro(struct module *mod)
> > 
> > Honestly, I find both the function names above horrible and not really 
> > self-explanatory (especially the _ro_ro variant). At least comment, 
> > explaining what they are actually doing, or picking up a better name, 
> > would make the code much more self-explanatory in my eyes.
> 
> Being the patch author, naturally the function names make sense to me.

:)

> set_module_ro_ro() means "set the module's read-only area to have 
> read-only permissions."
>
> Do you have any suggestions for a better name?

I'd even say it's superfluous to have the functions at the first place, 
and just calling set_page_attributes() directly makes the intent clear 
enough already.

Thanks,

-- 
Jiri Kosina
SUSE Labs

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