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/[email protected] > Signed-off-by: Toshi Kani <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: "H. Peter Anvin" <[email protected]> > Cc: Borislav Petkov <[email protected]> > Cc: Luis R. Rodriguez <[email protected]> > Cc: Andy Lutomirski <[email protected]> > Cc: Dan Williams <[email protected]> > --- > 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
