x86/msr: explicitly handle AMD DE_CFG

Report LFENCE_SERIALISE unconditionally for DE_CFG on AMD hardware and
silently drop writes.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index a478b91f23ffd795c02d919522b3ba9e1b177f5a..74bf7d95896678d9f46efdc9130908012209a10a 100644 (file)
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -292,6 +292,12 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
         *val = msrs->tsc_aux;
         break;
 
+    case MSR_AMD64_DE_CFG:
+        if ( !(cp->x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON)) )
+            goto gp_fault;
+        *val = AMD64_DE_CFG_LFENCE_SERIALISE;
+        break;
+
     case MSR_AMD64_DR0_ADDRESS_MASK:
     case MSR_AMD64_DR1_ADDRESS_MASK ... MSR_AMD64_DR3_ADDRESS_MASK:
         if ( !cp->extd.dbext )
@@ -517,6 +523,15 @@ int guest_wrmsr(struct vcpu *v, uint32_t msr, uint64_t val)
             wrmsr_tsc_aux(val);
         break;
 
+    case MSR_AMD64_DE_CFG:
+        /*
+         * OpenBSD 6.7 will panic if writing to DE_CFG triggers a #GP:
+         * https://www.illumos.org/issues/12998 - drop writes.
+         */
+        if ( !(cp->x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON)) )
+            goto gp_fault;
+        break;
+
     case MSR_AMD64_DR0_ADDRESS_MASK:
     case MSR_AMD64_DR1_ADDRESS_MASK ... MSR_AMD64_DR3_ADDRESS_MASK:
         if ( !cp->extd.dbext || val != (uint32_t)val )