soc/intel/apollolake: Move privilege drop to later stage

Previously privilege drop was happening "too early" and that caused some
PMC IPC programming (performed in FSP) to fail because sideband was
already locked out. This change set moves privilege drop to later stage,
after last FSP notify call.

BRANCH=reef
BUG=chrome-os-partner:60657
TEST=iotools rdmsr X 0x121, make sure they can't be read.
Also dmesg|grep -i IPC to make sure there are no errors related

Change-Id: Ia3a774aee5fbf92805a5c69093bfbd3d7682c3a7
Signed-off-by: Andrey Petrov <andrey.petrov@intel.com>
Reviewed-on: https://review.coreboot.org/17769
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

4 files changed, 21 insertions, 5 deletions

diff --git a/src/soc/intel/apollolake/Kconfig b/src/soc/intel/apollolake/Kconfig
index 6769af0d0a..b37cde678f 100644
--- a/src/soc/intel/apollolake/Kconfig
+++ b/src/soc/intel/apollolake/Kconfig
@@ -36,6 +36,7 @@ config CPU_SPECIFIC_OPTIONS
 	select NO_FIXED_XIP_ROM_SIZE
 	select NO_XIP_EARLY_STAGES
 	select PARALLEL_MP
+	select PARALLEL_MP_AP_WORK
 	select PCIEXP_ASPM
 	select PCIEXP_COMMON_CLOCK
 	select PCIEXP_CLK_PM
diff --git a/src/soc/intel/apollolake/chip.c b/src/soc/intel/apollolake/chip.c
index 171e01e930..a24ca33530 100644
--- a/src/soc/intel/apollolake/chip.c
+++ b/src/soc/intel/apollolake/chip.c
@@ -21,6 +21,7 @@
 #include <cbmem.h>
 #include <console/console.h>
 #include <cpu/cpu.h>
+#include <cpu/x86/mp.h>
 #include <device/device.h>
 #include <device/pci.h>
 #include <fsp/api.h>
@@ -499,11 +500,26 @@ struct chip_operations soc_intel_apollolake_ops = {
 	.final = &soc_final
 };
 
+static void drop_privilege_all(void)
+{
+	/* Drop privilege level on all the CPUs */
+	if (mp_run_on_all_cpus(&enable_untrusted_mode, 1000) < 0)
+		printk(BIOS_ERR, "failed to enable untrusted mode\n");
+}
+
 void platform_fsp_notify_status(enum fsp_notify_phase phase)
 {
-	/* Hide the P2SB device to align with previous behavior. */
-	if (phase == END_OF_FIRMWARE)
+	if (phase == END_OF_FIRMWARE) {
+		/* Hide the P2SB device to align with previous behavior. */
 		p2sb_hide();
+		/*
+		 * As per guidelines BIOS is recommended to drop CPU privilege
+		 * level to IA_UNTRUSTED. After that certain device registers
+		 * and MSRs become inaccessible supposedly increasing system
+		 * security.
+		 */
+		drop_privilege_all();
+	}
 }
 
 /*
diff --git a/src/soc/intel/apollolake/cpu.c b/src/soc/intel/apollolake/cpu.c
index 8b8f963e4c..ff300bcc90 100644
--- a/src/soc/intel/apollolake/cpu.c
+++ b/src/soc/intel/apollolake/cpu.c
@@ -53,7 +53,7 @@ static const struct reg_script core_msr_script[] = {
 	REG_SCRIPT_END
 };
 
-static void enable_untrusted_mode(void)
+void enable_untrusted_mode(void)
 {
 	msr_t msr = rdmsr(MSR_POWER_MISC);
 	msr.lo |= ENABLE_IA_UNTRUSTED;
@@ -70,8 +70,6 @@ static void soc_core_init(device_t cpu)
 	 * implemented in microcode.
 	*/
 	enable_pm_timer_emulation();
-	/* Drop privilege level */
-	enable_untrusted_mode();
 }
 
 static struct device_operations cpu_dev_ops = {
diff --git a/src/soc/intel/apollolake/include/soc/cpu.h b/src/soc/intel/apollolake/include/soc/cpu.h
index db9d3dde05..b4c86842ba 100644
--- a/src/soc/intel/apollolake/include/soc/cpu.h
+++ b/src/soc/intel/apollolake/include/soc/cpu.h
@@ -24,6 +24,7 @@
 
 void apollolake_init_cpus(struct device *dev);
 void set_max_freq(void);
+void enable_untrusted_mode(void);
 #endif
 
 #define CPUID_APOLLOLAKE_A0	0x506c8