[PATCH 2/2] x86/xen: during early setup, only 1:1 map the ISA region

[David Vrabel <david.vrabel@citrix.com>]

From: David Vrabel <david.vrabel@citrix.com>

During early setup, when the reserved regions and MMIO holes are being
setup as 1:1 in the p2m, clear any mappings instead of making them 1:1
(execept for the ISA region which is expected to be mapped).

This reverts a change in behaviour introduced in 3.5 by 83d51ab473dd
(xen/setup: update VA mapping when releasing memory during setup).

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 arch/x86/xen/setup.c |   16 +++++++++++-----
 1 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 5a093b7..081292e 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -215,13 +215,19 @@ static void __init xen_set_identity_and_release_chunk(
 	unsigned long pfn;
 
 	/*
-	 * If the PFNs are currently mapped, the VA mapping also needs
-	 * to be updated to be 1:1.
+	 * If the PFNs are currently mapped, clear the mappings
+	 * (except for the ISA region which must be 1:1 mapped) to
+	 * release the refcounts (in Xen) on the original frames.
 	 */
-	for (pfn = start_pfn; pfn <= max_pfn_mapped && pfn < end_pfn; pfn++)
+	for (pfn = start_pfn; pfn <= max_pfn_mapped && pfn < end_pfn; pfn++) {
+		pte_t pte = __pte_ma(0);
+
+		if (pfn < PFN_UP(ISA_END_ADDRESS))
+			pte = mfn_pte(pfn, PAGE_KERNEL_IO);
+
 		(void)HYPERVISOR_update_va_mapping(
-			(unsigned long)__va(pfn << PAGE_SHIFT),
-			mfn_pte(pfn, PAGE_KERNEL_IO), 0);
+			(unsigned long)__va(pfn << PAGE_SHIFT), pte, 0);
+	}
 
 	if (start_pfn < nr_pages)
 		*released += xen_release_chunk(
-- 
1.7.2.5