[PATCH] Fix kunmap_atomic's use of kpte_clear_flush()

[PATCH] Fix kunmap_atomic's use of kpte_clear_flush()

[Jeremy Fitzhardinge]

kunmap_atomic() will call kpte_clear_flush with vaddr/ptep arguments
which don't correspond if the vaddr is just a normal lowmem address
(ie, not in the KMAP area).  This patch makes sure that the pte is
only cleared if kmap area was actually used for the mapping.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Zachary Amsden <zach@vmware.com>

===================================================================
--- a/arch/i386/mm/highmem.c
+++ b/arch/i386/mm/highmem.c
@@ -56,22 +56,20 @@ void kunmap_atomic(void *kvaddr, enum km
 	unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
 	enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();
 
-#ifdef CONFIG_DEBUG_HIGHMEM
-	if (vaddr >= PAGE_OFFSET && vaddr < (unsigned long)high_memory) {
-		pagefault_enable();
-		return;
-	}
-
-	if (vaddr != __fix_to_virt(FIX_KMAP_BEGIN+idx))
-		BUG();
-#endif
 	/*
 	 * Force other mappings to Oops if they'll try to access this pte
 	 * without first remap it.  Keeping stale mappings around is a bad idea
 	 * also, in case the page changes cacheability attributes or becomes
 	 * a protected page in a hypervisor.
 	 */
-	kpte_clear_flush(kmap_pte-idx, vaddr);
+	if (vaddr == __fix_to_virt(FIX_KMAP_BEGIN+idx))
+		kpte_clear_flush(kmap_pte-idx, vaddr);
+	else {
+#ifdef CONFIG_DEBUG_HIGHMEM
+		BUG_ON(vaddr < PAGE_OFFSET);
+		BUG_ON(vaddr >= (unsigned long)high_memory);
+#endif
+	}
 
 	pagefault_enable();
 }

Re: [PATCH] Fix kunmap_atomic's use of kpte_clear_flush()

[Zachary Amsden]

Jeremy Fitzhardinge wrote:
> kunmap_atomic() will call kpte_clear_flush with vaddr/ptep arguments
> which don't correspond if the vaddr is just a normal lowmem address
> (ie, not in the KMAP area).  This patch makes sure that the pte is
> only cleared if kmap area was actually used for the mapping.
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Zachary Amsden <zach@vmware.com>

Ack.

Re: [PATCH] Fix kunmap_atomic's use of kpte_clear_flush()

[Rusty Russell]

On Tue, 2006-11-07 at 16:22 -0800, Jeremy Fitzhardinge wrote:
> kunmap_atomic() will call kpte_clear_flush with vaddr/ptep arguments
> which don't correspond if the vaddr is just a normal lowmem address
> (ie, not in the KMAP area).  This patch makes sure that the pte is
> only cleared if kmap area was actually used for the mapping.

Or in other words, if kmap_atomic() does nothing, kunmap_atomic() should
do nothing.

Rusty.

Re: [PATCH] Fix kunmap_atomic's use of kpte_clear_flush()

[Jeremy Fitzhardinge]

Rusty Russell wrote:
> On Tue, 2006-11-07 at 16:22 -0800, Jeremy Fitzhardinge wrote:
>   
>> kunmap_atomic() will call kpte_clear_flush with vaddr/ptep arguments
>> which don't correspond if the vaddr is just a normal lowmem address
>> (ie, not in the KMAP area).  This patch makes sure that the pte is
>> only cleared if kmap area was actually used for the mapping.
>>     
>
> Or in other words, if kmap_atomic() does nothing, kunmap_atomic() should
> do nothing.
>   

Sure.  I guess there's no particular reason why kmap_atomic() couldn't 
always map, but I guess avoid the pagetable updates is worthwhile.

    J