[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@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Luis R. Rodriguez <mcgrof@xxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 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;
 	}