Re: [Xen-devel] [PATCH] wrong accounting in direct_remap_pfn_range

[Steven Rostedt <srostedt@xxxxxxxxxx>]

Keir Fraser wrote:
> On 31/8/06 1:37 am, "Steven Rostedt" <srostedt@xxxxxxxxxx> 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@xxxxxxxxxx>


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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