linux-kernel - Re: [PATCH] x86/mm: Add warning to ioremap() for conflicting cache type

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Date:	Wed, 25 May 2016 19:34:27 +0000
From:	"Kani, Toshimitsu" <toshi.kani@....com>
To:	"mcgrof@...nel.org" <mcgrof@...nel.org>
CC:	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hch@...radead.org" <hch@...radead.org>, "bp@...e.de" <bp@...e.de>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	"will.deacon@....com" <will.deacon@....com>,
	"luto@...nel.org" <luto@...nel.org>,
	"julia.lawall@...6.fr" <julia.lawall@...6.fr>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>
Subject: Re: [PATCH] x86/mm: Add warning to ioremap() for conflicting cache
 type

On Wed, 2016-05-25 at 01:33 +0200, Luis R. Rodriguez wrote:
> On Wed, Apr 27, 2016 at 09:25:57AM -0600, Toshi Kani wrote:
> > 
> > On x86, ioremap() and remap_pfn_range() fail on conflicting cache
> > type of an alias mapping request only if the case is not allowed
> > by the rule set in is_new_memtype_allowed(). While this exemption
> > is necessary for remap_pfn_range() called for /dev/mem mappings,
> > it is not necessary for ioremap().
>
> The wording here is a bit unclear. How about:

I will update the change log according to your suggestions.


> > Link: https://lkml.org/lkml/2016/4/16/54
>
> lkml.org references should be avoided, we have no control over
> that domain. Please instead use:
> 
> http://lkml.kernel.org/r/20160416092018.GA8453@gmail.com

Will do.

> > 
> > Signed-off-by: Toshi Kani <toshi.kani@....com>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: "H. Peter Anvin" <hpa@...or.com>
> > Cc: Borislav Petkov <bp@...e.de>
> > Cc: Luis R. Rodriguez <mcgrof@...e.com>
> > Cc: Andy Lutomirski <luto@...nel.org>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > ---
> >  arch/x86/mm/ioremap.c |   10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> > index 0d8d53d..16c5887 100644
> > --- a/arch/x86/mm/ioremap.c
> > +++ b/arch/x86/mm/ioremap.c
> > @@ -138,14 +138,16 @@ static void __iomem
> > *__ioremap_caller(resource_size_t phys_addr,
> >  	}
> >  
> >  	if (pcm != new_pcm) {
> > -		if (!is_new_memtype_allowed(phys_addr, size, pcm,
> > new_pcm)) {
> > -			printk(KERN_ERR
> > -		"ioremap error for 0x%llx-0x%llx, requested 0x%x, got
> > 0x%x\n",
> > +		retval = is_new_memtype_allowed(phys_addr, size, pcm,
> > new_pcm);
> > +		pr_err(
> > +		    "ioremap %s for 0x%llx-0x%llx, requested 0x%x, got
> > 0x%x\n",
> > +				retval ? "warning" : "error",
> >  				(unsigned long long)phys_addr,
> >  				(unsigned long long)(phys_addr +
> > size),
> >  				pcm, new_pcm);
>
> This doesn't really make it humanly consumable, a pcm_to_str may help,
> such use already exists but not generalized see pat_get_cache_mode().

OK, I will add a pcm_to_str.

> > 
> > +		if (!retval)
> >  			goto err_free_memtype;
> > -		}
> > +
> >  		pcm = new_pcm;
> >  	}
>
> In the future we may be able to proactively hunt for these invalid uses
> semantically but to do so we need first a demo driver with all known
> possible bugs we can think of.

Right.

Thanks,
-Toshi