[Xen-devel] [PATCH] Stop clobbering AMD TSC offsets

[Ben Guthro <bguthro@xxxxxxxxxxxxxxx>]

This fixes a bug in which HVM VCPUs running on AMD have their TSC
offset clobbered (to zero) when they switch to real mode.  The
consequences of this are nearly unnoticeable in most cases, but the
AMD folks (Tom Woller & Travis Betak) agree this is a (minor) bug and
have been waiting forever for me to port and post this so they can
strike it off their TODO lists.

Signed-off-by: David Lively <dlively@xxxxxxxxxxxxxxx>
Signed-off-by: Ben Guthro <bguthro@xxxxxxxxxxxxxxx>

diff -r c03c4be32469 xen/arch/x86/hvm/svm/svm.c
--- a/xen/arch/x86/hvm/svm/svm.c        Thu Jul 12 14:31:51 2007 -0400
+++ b/xen/arch/x86/hvm/svm/svm.c        Thu Jul 12 14:31:51 2007 -0400
@@ -2329,9 +2329,6 @@ static int svm_reset_to_realmode(struct 
     /* clear the vmcb and user regs */
     memset(regs, 0, sizeof(struct cpu_user_regs));
    
-    /* VMCB Control */
-    vmcb->tsc_offset = 0;
-
     /* VMCB State */
     vmcb->cr0 = X86_CR0_ET | X86_CR0_PG | X86_CR0_WP;
     v->arch.hvm_svm.cpu_shadow_cr0 = X86_CR0_ET;

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