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

[David Vrabel <david.vrabel@xxxxxxxxxx>]

From: David Vrabel <david.vrabel@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 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


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