[PATCH v3] x86/msr: handle reads to MSR_P5_MC_{ADDR,TYPE}

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Windows Server 2019 Essentials will unconditionally attempt to read
P5_MC_ADDR MSR at boot and throw a BSOD if injected a #GP.

Fix this by mapping MSR_P5_MC_{ADDR,TYPE} to
MSR_IA32_MCi_{ADDR,STATUS}, as reported also done by hardware in Intel
SDM "Mapping of the Pentium Processor Machine-Check Errors to the
Machine-Check Architecture" section.

Reported-by: Steffen Einsle <einsle@xxxxxxxxxx>
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v2:
 - Use fallthrough pseudo keyword.
 - Expand comment about bank 0 quirk.
 - Change condition for early exit from vmce_intel_rdmsr.

Changes since v1:
 - Implement in vmce_rdmsr.
---
 xen/arch/x86/cpu/mcheck/mce.h        |  6 ++++++
 xen/arch/x86/cpu/mcheck/mce_intel.c  | 19 +++++++++++++++++++
 xen/arch/x86/cpu/mcheck/vmce.c       |  2 ++
 xen/arch/x86/include/asm/msr-index.h |  3 +++
 xen/arch/x86/msr.c                   |  2 ++
 5 files changed, 32 insertions(+)

diff --git a/xen/arch/x86/cpu/mcheck/mce.h b/xen/arch/x86/cpu/mcheck/mce.h
index 535d0abf8f..bea08bdc74 100644
--- a/xen/arch/x86/cpu/mcheck/mce.h
+++ b/xen/arch/x86/cpu/mcheck/mce.h
@@ -169,6 +169,12 @@ static inline int mce_vendor_bank_msr(const struct vcpu 
*v, uint32_t msr)
         if (msr >= MSR_IA32_MC0_CTL2 &&
             msr < MSR_IA32_MCx_CTL2(v->arch.vmce.mcg_cap & MCG_CAP_COUNT) )
             return 1;
+        fallthrough;
+
+    case X86_VENDOR_CENTAUR:
+    case X86_VENDOR_SHANGHAI:
+        if (msr == MSR_P5_MC_ADDR || msr == MSR_P5_MC_TYPE)
+            return 1;
         break;
 
     case X86_VENDOR_AMD:
diff --git a/xen/arch/x86/cpu/mcheck/mce_intel.c 
b/xen/arch/x86/cpu/mcheck/mce_intel.c
index 50198e0c29..28a605a5cb 100644
--- a/xen/arch/x86/cpu/mcheck/mce_intel.c
+++ b/xen/arch/x86/cpu/mcheck/mce_intel.c
@@ -1008,8 +1008,27 @@ int vmce_intel_wrmsr(struct vcpu *v, uint32_t msr, 
uint64_t val)
 
 int vmce_intel_rdmsr(const struct vcpu *v, uint32_t msr, uint64_t *val)
 {
+    const struct cpuid_policy *cp = v->domain->arch.cpuid;
     unsigned int bank = msr - MSR_IA32_MC0_CTL2;
 
+    switch ( msr )
+    {
+    case MSR_P5_MC_ADDR:
+        /*
+         * Bank 0 is used for the 'bank 0 quirk' on older processors.
+         * See vcpu_fill_mc_msrs() for reference.
+         */
+        *val = v->arch.vmce.bank[1].mci_addr;
+        return 1;
+
+    case MSR_P5_MC_TYPE:
+        *val = v->arch.vmce.bank[1].mci_status;
+        return 1;
+    }
+
+    if ( !(cp->x86_vendor & X86_VENDOR_INTEL) )
+        return 0;
+
     if ( bank < GUEST_MC_BANK_NUM )
     {
         *val = v->arch.vmce.bank[bank].mci_ctl2;
diff --git a/xen/arch/x86/cpu/mcheck/vmce.c b/xen/arch/x86/cpu/mcheck/vmce.c
index 458120f9ad..af30811afd 100644
--- a/xen/arch/x86/cpu/mcheck/vmce.c
+++ b/xen/arch/x86/cpu/mcheck/vmce.c
@@ -150,6 +150,8 @@ static int bank_mce_rdmsr(const struct vcpu *v, uint32_t 
msr, uint64_t *val)
     default:
         switch ( boot_cpu_data.x86_vendor )
         {
+        case X86_VENDOR_CENTAUR:
+        case X86_VENDOR_SHANGHAI:
         case X86_VENDOR_INTEL:
             ret = vmce_intel_rdmsr(v, msr, val);
             break;
diff --git a/xen/arch/x86/include/asm/msr-index.h 
b/xen/arch/x86/include/asm/msr-index.h
index 3e038db618..31964b88af 100644
--- a/xen/arch/x86/include/asm/msr-index.h
+++ b/xen/arch/x86/include/asm/msr-index.h
@@ -15,6 +15,9 @@
  * abbreviated name.  Exceptions will be considered on a case-by-case basis.
  */
 
+#define MSR_P5_MC_ADDR                      0
+#define MSR_P5_MC_TYPE                      0x00000001
+
 #define MSR_APIC_BASE                       0x0000001b
 #define  APIC_BASE_BSP                      (_AC(1, ULL) <<  8)
 #define  APIC_BASE_EXTD                     (_AC(1, ULL) << 10)
diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index a1e268eea9..d87317e989 100644
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -283,6 +283,8 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
         *val = msrs->misc_features_enables.raw;
         break;
 
+    case MSR_P5_MC_ADDR:
+    case MSR_P5_MC_TYPE:
     case MSR_IA32_MCG_CAP     ... MSR_IA32_MCG_CTL:      /* 0x179 -> 0x17b */
     case MSR_IA32_MCx_CTL2(0) ... MSR_IA32_MCx_CTL2(31): /* 0x280 -> 0x29f */
     case MSR_IA32_MCx_CTL(0)  ... MSR_IA32_MCx_MISC(31): /* 0x400 -> 0x47f */
-- 
2.35.1