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authorjohn cooper <john.cooper@redhat.com>2011-01-21 00:21:00 -0500
committerMarcelo Tosatti <mtosatti@redhat.com>2011-03-17 13:08:27 -0300
commit91c9c3eda4f3066980d13a6907ef84f3a99364bd (patch)
treeb39e69fd1fff6f86b0b29269c29f83ded11aa46f
parent3cba41307a2b1344ab8c1b9f55202d1e9d7bf81b (diff)
KVM: x86: handle guest access to BBL_CR_CTL3 MSR
A correction to Intel cpu model CPUID data (patch queued) caused winxp to BSOD when booted with a Penryn model. This was traced to the CPUID "model" field correction from 6 -> 23 (as is proper for a Penryn class of cpu). Only in this case does the problem surface. The cause for this failure is winxp accessing the BBL_CR_CTL3 MSR which is unsupported by current kvm, appears to be a legacy MSR not fully characterized yet existing in current silicon, and is apparently carried forward in MSR space to accommodate vintage code as here. It is not yet conclusive whether this MSR implements any of its legacy functionality or is just an ornamental dud for compatibility. While I found no silicon version specific documentation link to this MSR, a general description exists in Intel's developer's reference which agrees with the functional behavior of other bootloader/kernel code I've examined accessing BBL_CR_CTL3. Regrettably winxp appears to be setting bit #19 called out as "reserved" in the above document. So to minimally accommodate this MSR, kvm msr get will provide the equivalent mock data and kvm msr write will simply toss the guest passed data without interpretation. While this treatment of BBL_CR_CTL3 addresses the immediate problem, the approach may be modified pending clarification from Intel. Signed-off-by: john cooper <john.cooper@redhat.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
-rw-r--r--arch/x86/include/asm/msr-index.h1
-rw-r--r--arch/x86/kvm/x86.c19
2 files changed, 20 insertions, 0 deletions
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 823d4822340..fd5a1f365c9 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -43,6 +43,7 @@
#define MSR_MTRRcap 0x000000fe
#define MSR_IA32_BBL_CR_CTL 0x00000119
+#define MSR_IA32_BBL_CR_CTL3 0x0000011e
#define MSR_IA32_SYSENTER_CS 0x00000174
#define MSR_IA32_SYSENTER_ESP 0x00000175
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a7f65aa6eef..7faf262ab20 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1592,6 +1592,12 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
} else
return set_msr_hyperv(vcpu, msr, data);
break;
+ case MSR_IA32_BBL_CR_CTL3:
+ /* Drop writes to this legacy MSR -- see rdmsr
+ * counterpart for further detail.
+ */
+ pr_unimpl(vcpu, "ignored wrmsr: 0x%x data %llx\n", msr, data);
+ break;
default:
if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr))
return xen_hvm_config(vcpu, data);
@@ -1846,6 +1852,19 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
} else
return get_msr_hyperv(vcpu, msr, pdata);
break;
+ case MSR_IA32_BBL_CR_CTL3:
+ /* This legacy MSR exists but isn't fully documented in current
+ * silicon. It is however accessed by winxp in very narrow
+ * scenarios where it sets bit #19, itself documented as
+ * a "reserved" bit. Best effort attempt to source coherent
+ * read data here should the balance of the register be
+ * interpreted by the guest:
+ *
+ * L2 cache control register 3: 64GB range, 256KB size,
+ * enabled, latency 0x1, configured
+ */
+ data = 0xbe702111;
+ break;
default:
if (!ignore_msrs) {
pr_unimpl(vcpu, "unhandled rdmsr: 0x%x\n", msr);