x86: suppress BTI mitigations around S3 suspend/resume

NMI and #MC can occur at any time after S3 resume, yet the MSR_SPEC_CTRL
may become available only once we're reloaded microcode. Make
SPEC_CTRL_ENTRY_FROM_INTR_IST and DO_SPEC_CTRL_EXIT_TO_XEN no-ops for
the critical period of time.

Also set the MSR back to its intended value.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
x86: Use spec_ctrl_{enter,exit}_idle() in the S3/S5 path

The main purpose of this patch is to avoid opencoding the recovery logic at
the end, but also has the positive side effect of relaxing the SPEC_CTRL
mitigations when working to shut the final CPU down.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 710a8ebf2bc111a34bba04d1c85b6d07ed3d9389
master date: 2018-04-16 14:09:55 +0200
master commit: ef3ab46493f650b7e5cca2b2578a99ca0cbff195
master date: 2018-04-19 10:55:59 +0100

diff --git a/xen/arch/x86/acpi/power.c b/xen/arch/x86/acpi/power.c
index a66049109e2667de9bb5a1b659883fcf66b7f6d6..87cc09ee46b839ed34ff574037bf1147d91f614b 100644 (file)
--- a/xen/arch/x86/acpi/power.c
+++ b/xen/arch/x86/acpi/power.c
@@ -29,6 +29,7 @@
 #include <asm/tboot.h>
 #include <asm/apic.h>
 #include <asm/io_apic.h>
+#include <asm/spec_ctrl.h>
 #include <acpi/cpufreq/cpufreq.h>
 
 uint32_t system_reset_counter = 1;
@@ -130,6 +131,7 @@ static int enter_state(u32 state)
 {
     unsigned long flags;
     int error;
+    struct cpu_info *ci;
     unsigned long cr4;
 
     if ( (state <= ACPI_STATE_S0) || (state > ACPI_S_STATES_MAX) )
@@ -173,6 +175,11 @@ static int enter_state(u32 state)
         goto done;
     }
 
+    ci = get_cpu_info();
+    spec_ctrl_enter_idle(ci);
+    /* Avoid NMI/#MC using MSR_SPEC_CTRL until we've reloaded microcode. */
+    ci->bti_ist_info = 0;
+
     ACPI_FLUSH_CPU_CACHE();
 
     switch ( state )
@@ -212,6 +219,10 @@ static int enter_state(u32 state)
 
     microcode_resume_cpu(0);
 
+    /* Re-enabled default NMI/#MC use of MSR_SPEC_CTRL. */
+    ci->bti_ist_info = default_bti_ist_info;
+    spec_ctrl_exit_idle(ci);
+
  done:
     spin_debug_enable();
     local_irq_restore(flags);