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

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

[Toshi Kani]

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(). Drivers should never call
ioremap() with a conflicting cache type. This exemption handling
may hide possible bugs in drivers.

Add a warning message to ioremap() when a conflicting cache type
is allowed by is_new_memtype_allowed(). This helps us identify
such usages in drivers.

There is no change in the behavior.

Link: https://lkml.org/lkml/2016/4/16/54
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.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);
+		if (!retval)
 			goto err_free_memtype;
-		}
+
 		pcm = new_pcm;
 	}
 

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

[Luis R. Rodriguez]

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:

Currently we allow for conflicting cache requests to account for
reading out /dev/mem, however /dev/mem uses remap_pfn_range(). An
explicit exception is not currently known to exist for conflicting
cache type requests for ioremap(), however we are not certain if
such conflicting use type currently does exist.

> Drivers should never call
> ioremap() with a conflicting cache type. This exemption handling
> may hide possible bugs in drivers.

And this to:

Upon review, we've determined that at least device drivers have
no business in calling ioremap() with a conflicting cache type.

> Add a warning message to ioremap() when a conflicting cache type
> is allowed by is_new_memtype_allowed(). This 

will help us

> helps us identify
> such usages in drivers.

such valid uses in device drivers

> 
> There is no change in the behavior.

There are no functional changes introduced by this commit other than
the addition of the new warning.

> 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

> Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Luis R. Rodriguez <mcgrof@suse.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Dan Williams <dan.j.williams@intel.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().

> +		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.

  Luis

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

[Kani, Toshimitsu]

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@hpe.com>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Cc: Borislav Petkov <bp@suse.de>
> > Cc: Luis R. Rodriguez <mcgrof@suse.com>
> > Cc: Andy Lutomirski <luto@kernel.org>
> > Cc: Dan Williams <dan.j.williams@intel.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