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

Steffen Persvold
2002-01-06T11:02:01Z

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,
--
Steffen Persvold | Scalable Linux Systems | Try out the world's best
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