Re: [PATCH] wrong accounting in direct_remap_pfn_range

[Steven Rostedt <srostedt@redhat.com>]

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Keir Fraser wrote:
> On 31/8/06 1:37 am, "Steven Rostedt" <srostedt@redhat.com> wrote:
> 
>> grr, I take it back, I am the one that's confused :P
>>
>> OK, this all happens because this whole blob of code is crazy because it
>> is missing a "if (size == 0)" check!
> 
> It's not really missing. We could have a size==0 check *or* we can have the
> v!=u check. We don't need both and I think the latter is more obviously
> correct, as the test is closer to the code that it 'protects'. Also it's a
> fairly idiomatic way of generating and flushing batches of work.
>

So what is really wrong with this code?  Or is the flushes need even on 
size == 0?

-- Steve

Signed-off-by: Steven Rostedt <srostedt@redhat.com>



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Index: linux-2.6-xen-sparse/arch/i386/mm/ioremap-xen.c
===================================================================
--- linux-2.6-xen-sparse.orig/arch/i386/mm/ioremap-xen.c
+++ linux-2.6-xen-sparse/arch/i386/mm/ioremap-xen.c
@@ -56,6 +56,9 @@ static int __direct_remap_pfn_range(stru
 	unsigned long i, start_address;
 	mmu_update_t *u, *v, *w;
 
+	if (unlikely(!size))
+		return 0;
+
 	u = v = w = (mmu_update_t *)__get_free_page(GFP_KERNEL|__GFP_REPEAT);
 	if (u == NULL)
 		return -ENOMEM;
@@ -91,17 +94,15 @@ static int __direct_remap_pfn_range(stru
 		v++;
 	}
 
-	if (v != u) {
-		/* get the ptep's filled in */
-		rc = apply_to_page_range(mm, start_address,
-					 address - start_address,
-					 direct_remap_area_pte_fn, &w);
-		if (rc)
-			goto out;
-		rc = -EFAULT;
-		if (unlikely(HYPERVISOR_mmu_update(u, v - u, NULL, domid) < 0))
-			goto out;
-	}
+	/* get the ptep's filled in */
+	rc = apply_to_page_range(mm, start_address,
+				 address - start_address,
+				 direct_remap_area_pte_fn, &w);
+	if (rc)
+		goto out;
+	rc = -EFAULT;
+	if (unlikely(HYPERVISOR_mmu_update(u, v - u, NULL, domid) < 0))
+		goto out;
 
 	rc = 0;
 

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