From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave McCracken <dcm@mccr.org>
Subject: [PATCH xen-unstable] Remove PSE flag from guest CR4
Date: Mon, 14 Sep 2009 12:27:16 -0500
Message-ID: <200909141227.16852.dcm@mccr.org>
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To: Xen Developers List <xen-devel@lists.xensource.com>, Keir Fraser <Keir.Fraser@eu.citrix.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
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When I originally did the Xen hypervisor hugepage patch I also allowed guests 
to see the PSE flag in CR4.  This has proven to be a mistake.  Here is a patch 
to remove that functionality.

All Linux kernels will still allow userspace hugepages without the flag.

Dave McCracken

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--- xen-unstable/./xen/arch/x86/traps.c	2009-09-14 12:15:46.000000000 -0500
+++ xen-hpage/./xen/arch/x86/traps.c	2009-09-14 12:18:42.000000000 -0500
@@ -752,8 +752,7 @@ static void pv_cpuid(struct cpu_user_reg
         __clear_bit(X86_FEATURE_VME, &d);
         if ( !cpu_has_apic )
             __clear_bit(X86_FEATURE_APIC, &d);
-        if ( !opt_allow_hugepage )
-            __clear_bit(X86_FEATURE_PSE, &d);
+        __clear_bit(X86_FEATURE_PSE, &d);
         __clear_bit(X86_FEATURE_PGE, &d);
         __clear_bit(X86_FEATURE_PSE36, &d);
     }
@@ -2064,12 +2063,9 @@ static int emulate_privileged_op(struct 
         case 4: /* Read CR4 */
             /*
              * Guests can read CR4 to see what features Xen has enabled. We
-             * therefore lie about PGE as it is unavailable to guests.
-             * Also disallow PSE if hugepages are not enabled.
+             * therefore lie about PGE and PSE as they are unavailable to guests.
              */
-            *reg = read_cr4() & ~X86_CR4_PGE;
-            if ( !opt_allow_hugepage )
-                *reg &= ~X86_CR4_PSE;
+            *reg = read_cr4() & ~(X86_CR4_PGE|X86_CR4_PSE);
             break;
 
         default:

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