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

--

yes, should be safe. Could you send a patch so that others can apply it

too?
	Ingo

--

Ofcourse :) :
Accept guest _PAGE_PWT page table entries, otherwise lguest will

always fail with a "bad page table entry" message.
Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>

---
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c

index 74b4cf2..952160b 100644

--- a/drivers/lguest/page_tables.c

+++ b/drivers/lguest/page_tables.c

@@ -178,8 +178,8 @@ static void release_pte(pte_t pte)
 static void check_gpte(struct lg_cpu *cpu, pte_t gpte)

 {

-	if ((pte_flags(gpte) & (_PAGE_PWT|_PAGE_PSE))

-	    || pte_pfn(gpte) >= cpu->lg->pfn_limit)

+	if ((pte_flags(gpte) & _PAGE_PSE) ||

+	    pte_pfn(gpte) >= cpu->lg->pfn_limit)

 		kill_guest(cpu, "bad page table entry");

 }
Regards,
--

Ahmed S. Darwish

Homepage: http://darwish.07.googlepages.com

Blog: http://darwish-07.blogspot.com

--

Thanks for tracking this Ahmed, and thanks to Ingo for pushing it upstream.
Cheers,

Rusty.

--

thanks - i've queued this up into x86.git. Rusty, is this fine to you,

and should we nurse this fix upstream?
	Ingo

--