Author: kib
Date: Fri Nov 9 16:00:30 2012
New Revision: 242828
URL: http://svnweb.freebsd.org/changeset/base/242828
Log:
Do not try to enable new features in the %cr4 if running under
hypervisor. Apparently, hypervisors failed to filter out 'Standard
Extended Features' report from CPUID, but deliver #gp when
corresponding bit in %cr4 is toggled.
This shall be reconsidered later, after hypervisors correct the bug.
Reported and tested by: joel
Reviewed by: avg
MFC after: 2 weeks
Modified:
head/sys/amd64/amd64/identcpu.c
Modified: head/sys/amd64/amd64/identcpu.c
==============================================================================
--- head/sys/amd64/amd64/identcpu.c Fri Nov 9 15:29:52 2012
(r242827)
+++ head/sys/amd64/amd64/identcpu.c Fri Nov 9 16:00:30 2012
(r242828)
@@ -481,7 +481,7 @@ SYSINIT(hook_tsc_freq, SI_SUB_CONFIGURE,
void
identify_cpu(void)
{
- u_int regs[4];
+ u_int regs[4], cpu_stdext_disable;
do_cpuid(0, regs);
cpu_high = regs[0];
@@ -516,6 +516,20 @@ identify_cpu(void)
if (cpu_high >= 7) {
cpuid_count(7, 0, regs);
cpu_stdext_feature = regs[1];
+
+ /*
+ * Some hypervisors fail to filter out unsupported
+ * extended features. For now, disable the
+ * extensions, activation of which requires setting a
+ * bit in CR4, and which VM monitors do not support.
+ */
+ if (cpu_feature2 & CPUID2_HV) {
+ cpu_stdext_disable = CPUID_STDEXT_FSGSBASE |
+ CPUID_STDEXT_SMEP;
+ } else
+ cpu_stdext_disable = 0;
+ TUNABLE_INT_FETCH("hw.cpu_stdext_disable", &cpu_stdext_disable);
+ cpu_stdext_feature &= ~cpu_stdext_disable;
}
if (cpu_vendor_id == CPU_VENDOR_INTEL ||
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