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

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

On 15/07/13 18:29, David Vrabel wrote:
> 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 fixes a regression introduced in 3.5 by 83d51ab473dd (xen/setup:
> update VA mapping when releasing memory during setup) which caused
> hosts with tboot to fail to boot.
> 
> tboot marks a region in the e820 map as unusable and the dom0 kernel
> would attempt to map this region and Xen does not permit unusable
> regions to be mapped by guests.

Don't apply this one just yet as it can cause boot crashes in
find_ibft_region() on certain machines (depending on their e820).

Best hold off until I can put it through a few more machines in our lab.

The fixed patch is:

--- 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(

David