Re: [Linux-ia64] Re: Status on ioremap patch

[Steffen Persvold <sp@scali.no>]

Keith Owens wrote:
> 
> On Sat, 05 Jan 2002 16:01:29 +0100,
> Steffen Persvold <sp@scali.no> wrote:
> >--- linux-2.4.17/mm/memory.c.orig      Fri Dec 21 18:42:05 2001
> >+++ linux-2.4.17/mm/memory.c   Sat Jan  5 13:13:26 2002
> >@@ -791,6 +791,9 @@
> >  * maps a range of physical memory into the requested pages. the old
> >  * mappings are removed. any references to nonexistent pages results
> >  * in null mappings (currently treated as "copy-on-access")
> >+ *
> >+ * For physical (or I/O) memory mapped into the kernel virtual space,
> >+ * the old mappings will not be removed.
> 
> That comment worries me.  If you have multiple mappings for the same
> page then you may have problems on hardware that uses virtually indexed
> caches.  Two virtual addresses could map to the same physical page but
> index to different cache lines, destroying cache coherency.  How do you
> prevent that?
> 

Well, actually multiple mappings in kernel space is denied :

+               if (address > VMALLOC_START && address < VMALLOC_END) {
+                       if (!pte_none(*pte)) {
+                               printk("remap_area_pte: page already exists\n");
+                               BUG();
+                       }
+                       set_pte(pte, mk_pte_phys(phys_addr, prot));
+               } else {
+                       struct page *page;
+                       pte_t oldpage;
+                       oldpage = ptep_get_and_clear(pte);
+
+                       page = virt_to_page(__va(phys_addr));
+                       if ((!VALID_PAGE(page)) || PageReserved(page))
+                               set_pte(pte, mk_pte_phys(phys_addr, prot));
+                       forget_pte(oldpage);
+               }

Regards,
-- 
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