OS-7125 Need mitigation of L1TF (CVE-2018-3646)
Reviewed by: Robert Mustacchi <rm@joyent.com>
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>

*** 2118,2127 ****
--- 2118,2140 ----
          cpi->cpi_nthread_bits = ddi_fls(cpi->cpi_ncpu_per_chip /
              cpi->cpi_ncore_per_chip);
  }
  
  static void
+ spec_l1d_flush_noop(void)
+ {
+ }
+ 
+ static void
+ spec_l1d_flush_msr(void)
+ {
+         wrmsr(MSR_IA32_FLUSH_CMD, IA32_FLUSH_CMD_L1D);
+ }
+ 
+ void (*spec_l1d_flush)(void) = spec_l1d_flush_noop;
+ 
+ static void
  cpuid_scan_security(cpu_t *cpu, uchar_t *featureset)
  {
          struct cpuid_info *cpi = cpu->cpu_m.mcpu_cpi;
  
          if (cpi->cpi_vendor == X86_VENDOR_AMD &&
*** 2202,2211 ****
--- 2215,2261 ----
                          add_x86_feature(featureset, X86FSET_SSBD);
  
                  if (ecp->cp_edx & CPUID_INTC_EDX_7_0_FLUSH_CMD)
                          add_x86_feature(featureset, X86FSET_FLUSH_CMD);
          }
+ 
+         if (cpu->cpu_id != 0)
+                 return;
+ 
+         /*
+          * We're the boot CPU, so let's figure out our L1TF status.
+          *
+          * First, if this is a RDCL_NO CPU, then we are not vulnerable: we don't
+          * need to exclude with ht_acquire(), and we don't need to flush.
+          */
+         if (is_x86_feature(featureset, X86FSET_RDCL_NO)) {
+                 extern int ht_exclusion;
+                 ht_exclusion = 0;
+                 spec_l1d_flush = spec_l1d_flush_noop;
+                 membar_producer();
+                 return;
+         }
+ 
+         /*
+          * If HT is enabled, we will need HT exclusion, as well as the flush on
+          * VM entry.  If HT isn't enabled, we still need at least the flush for
+          * the L1TF sequential case.
+          *
+          * However, if X86FSET_L1D_VM_NO is set, we're most likely running
+          * inside a VM ourselves, and we don't need the flush.
+          *
+          * If we don't have the FLUSH_CMD available at all, we'd better just
+          * hope HT is disabled.
+          */
+         if (is_x86_feature(featureset, X86FSET_FLUSH_CMD) &&
+             !is_x86_feature(featureset, X86FSET_L1D_VM_NO)) {
+                 spec_l1d_flush = spec_l1d_flush_msr;
+         } else {
+                 spec_l1d_flush = spec_l1d_flush_noop;
+         }
+ 
+         membar_producer();
  }
  
  /*
   * Setup XFeature_Enabled_Mask register. Required by xsave feature.
   */