[Xen-changelog] Emulate guest reads of CR4, masking features that Xen

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID 89b1b67fc2c4111d6eece1adab8dbcfae6dd069f
# Parent  438f1b53682b8b796be5374e5f148f0617829a28
Emulate guest reads of CR4, masking features that Xen
does not export to guests.

Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>

diff -r 438f1b53682b -r 89b1b67fc2c4 xen/arch/x86/traps.c
--- a/xen/arch/x86/traps.c      Wed Oct  5 15:32:07 2005
+++ b/xen/arch/x86/traps.c      Wed Oct  5 15:54:09 2005
@@ -895,6 +895,14 @@
             *reg = pagetable_get_paddr(v->arch.guest_table);
             break;
 
+        case 4: /* Read CR4 */
+            /*
+             * Guests can read CR4 to see what features Xen has enabled. We
+             * therefore lie about PGE & PSE as they are unavailable to guests.
+             */
+            *reg = read_cr4() & ~(X86_CR4_PGE|X86_CR4_PSE);
+            break;
+
         default:
             goto fail;
         }

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