[Lguest/x86]: Clash with ioremap_nocache() + _PAGE_PWT

Ahmed S. Darwish
2008-02-06T23:24:23Z

Hi all,

Beginning from commit 4138cc3418f5, ioremap_nocache() sets the _PAGE_PWT
flag.

Lguest doesn't accept a guest pte with a _PWT flag and reports a
"bad page table entry" in that case.

I've removed check from lguest code and everything worked fine.
Is this safe from the Lguest side ?

Mentioned commit [*]:

commit 4138cc3418f5eaa7524ff8e927102863f1ba0ea5
Author: Siddha, Suresh B <suresh.b.siddha@intel.com>
Date: Wed Jan 30 13:33:43 2008 +0100

x86: set strong uncacheable where UC is really desired

Also use _PAGE_PWT for all the mappings which need uncache mapping.
Instead of existing PAT2 which is UC- (and can be overwritten by MTRRs),
we now use PAT3 which is strong uncacheable.

This makes it consistent with pgprot_noncached()

diff --git a/arch/x86/mm/ioremap_32.c b/arch/x86/mm/ioremap_32.c
index 0b27831..ef0f6a4 100644
--- a/arch/x86/mm/ioremap_32.c
+++ b/arch/x86/mm/ioremap_32.c
@@ -119,7 +119,7 @@ EXPORT_SYMBOL(__ioremap);
void __iomem *ioremap_nocache (unsigned long phys_addr, unsigned long size)
{
unsigned long last_addr;
- void __iomem *p = __ioremap(phys_addr, size, _PAGE_PCD);
+ void __iomem *p = __ioremap(phys_addr, size, _PAGE_PCD | _PAGE_PWT);
if (!p)
return p;

Thanks,

[*]: latest pull calls set_memory_uc() which also sets the _PWT flag.

--
Ahmed S. Darwish
Homepage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com