From: Chris Lalancette <clalance@redhat.com>
Date: Fri, 20 Mar 2009 17:33:40 +0100
Subject: [mm] xen: 'ptwr_emulate' messages when booting PV guest
Message-id: 49C3C564.7080200@redhat.com
O-Subject: [RHEL5.4 PATCH]: Fix "ptwr_emulate" messages when booting i386 PV guest
Bugzilla: 490567
RH-Acked-by: Don Dutile <ddutile@redhat.com>
RH-Acked-by: Rik van Riel <riel@redhat.com>
RH-Acked-by: Gerd Hoffmann <kraxel@redhat.com>

All,
     Attached is a patch to fix a minor issue when booting an i386 PV guest.
Every time you boot this type of guest, you get the following message in the
hypervisor logs:

(XEN) mm.c:3335:d1 ptwr_emulate: fixing up invalid PAE PTE 00000000d6d8f025

What's going on is that while the guest is setting up it's fixmaps, it is doing
so via a straight set_pte() call.  In turn this first writes the high half of
the PAE PTE, then writes the low half; unfortunately the hypervisor expects it
to be done in the opposite order.  Luckily, the hypervisor has code to deal with
this situation, and fixes it up, but also prints the error message.  The
solution comes from upstream linux-2.6.18-xen.hg c/s 214; instead of doing a
set_pte (which does a trap-n-emulate), we do an explicit hypercall to set the
PTE instead.  This neatly sidesteps the issue, and gets rid of the warning on boot.
     Tested by me on an i686 guest; before the patch, I would see the above HV
message on every i686 boot, and after the patch, I no longer see the message.
     This should resolve BZ 490567.  Please review and ACK.

--
Chris Lalancette

diff --git a/arch/i386/mm/pgtable-xen.c b/arch/i386/mm/pgtable-xen.c
index 9d8e4cb..77638c8 100644
--- a/arch/i386/mm/pgtable-xen.c
+++ b/arch/i386/mm/pgtable-xen.c
@@ -75,81 +75,6 @@ void show_mem(void)
 }
 
 /*
- * Associate a virtual page frame with a given physical page frame 
- * and protection flags for that frame.
- */ 
-static void set_pte_pfn(unsigned long vaddr, unsigned long pfn, pgprot_t flags)
-{
-	pgd_t *pgd;
-	pud_t *pud;
-	pmd_t *pmd;
-	pte_t *pte;
-
-	pgd = swapper_pg_dir + pgd_index(vaddr);
-	if (pgd_none(*pgd)) {
-		BUG();
-		return;
-	}
-	pud = pud_offset(pgd, vaddr);
-	if (pud_none(*pud)) {
-		BUG();
-		return;
-	}
-	pmd = pmd_offset(pud, vaddr);
-	if (pmd_none(*pmd)) {
-		BUG();
-		return;
-	}
-	pte = pte_offset_kernel(pmd, vaddr);
-	/* <pfn,flags> stored as-is, to permit clearing entries */
-	set_pte(pte, pfn_pte(pfn, flags));
-
-	/*
-	 * It's enough to flush this one mapping.
-	 * (PGE mappings get flushed as well)
-	 */
-	__flush_tlb_one(vaddr);
-}
-
-/*
- * Associate a virtual page frame with a given physical page frame 
- * and protection flags for that frame.
- */ 
-static void set_pte_pfn_ma(unsigned long vaddr, unsigned long pfn,
-			   pgprot_t flags)
-{
-	pgd_t *pgd;
-	pud_t *pud;
-	pmd_t *pmd;
-	pte_t *pte;
-
-	pgd = swapper_pg_dir + pgd_index(vaddr);
-	if (pgd_none(*pgd)) {
-		BUG();
-		return;
-	}
-	pud = pud_offset(pgd, vaddr);
-	if (pud_none(*pud)) {
-		BUG();
-		return;
-	}
-	pmd = pmd_offset(pud, vaddr);
-	if (pmd_none(*pmd)) {
-		BUG();
-		return;
-	}
-	pte = pte_offset_kernel(pmd, vaddr);
-	/* <pfn,flags> stored as-is, to permit clearing entries */
-	set_pte(pte, pfn_pte_ma(pfn, flags));
-
-	/*
-	 * It's enough to flush this one mapping.
-	 * (PGE mappings get flushed as well)
-	 */
-	__flush_tlb_one(vaddr);
-}
-
-/*
  * Associate a large virtual page frame with a given physical page frame 
  * and protection flags for that frame. pfn is for the base of the page,
  * vaddr is what the page gets mapped to - both must be properly aligned. 
@@ -191,6 +116,7 @@ EXPORT_SYMBOL(__FIXADDR_TOP);
 void __set_fixmap (enum fixed_addresses idx, maddr_t phys, pgprot_t flags)
 {
 	unsigned long address = __fix_to_virt(idx);
+	pte_t pte;
 
 	if (idx >= __end_of_fixed_addresses) {
 		BUG();
@@ -201,12 +127,15 @@ void __set_fixmap (enum fixed_addresses idx, maddr_t phys, pgprot_t flags)
 #ifdef CONFIG_X86_F00F_BUG
 	case FIX_F00F_IDT:
 #endif
-		set_pte_pfn(address, phys >> PAGE_SHIFT, flags);
+		pte = pfn_pte(phys >> PAGE_SHIFT, flags);
 		break;
 	default:
-		set_pte_pfn_ma(address, phys >> PAGE_SHIFT, flags);
+		pte = pfn_pte_ma(phys >> PAGE_SHIFT, flags);
 		break;
 	}
+	if (HYPERVISOR_update_va_mapping(address, pte,
+					 UVMF_INVLPG|UVMF_ALL))
+		BUG();
 	nr_fixmaps++;
 }