Nico Huber has uploaded this change for review.

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cpu/x86/mp_init: Refactor and comment staggered SMBASE calculation

Change-Id: I98f55938f224ee49361d73e68ace9f9fcee7f48a
Signed-off-by: Nico Huber <nico.h@gmx.de>
---
M src/cpu/x86/mp_init.c
1 file changed, 8 insertions(+), 4 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/83/38783/1

diff --git a/src/cpu/x86/mp_init.c b/src/cpu/x86/mp_init.c
index 45f7337..77eb661 100644
--- a/src/cpu/x86/mp_init.c
+++ b/src/cpu/x86/mp_init.c
@@ -720,7 +720,7 @@
 	const struct smm_runtime *runtime;
 	int cpu;
 	uintptr_t curr_smbase;
-	uintptr_t perm_smbase;
+	uintptr_t staggered_smbase;
 
 	p = arg;
 	runtime = p->runtime;
@@ -737,9 +737,13 @@
 	 * The permanent handler runs with all cpus concurrently. Precalculate
 	 * the location of the new SMBASE. If using SMM modules then this
 	 * calculation needs to match that of the module loader.
+	 *
+	 * Hardware assumes SMM entry at SMM_ENTRY_OFFSET, memory below this
+	 * offset won't be accessed. `staggered_smbase` can point below actual
+	 * SMRAM, hence.
 	 */
-	perm_smbase = mp_state.perm_smbase;
-	perm_smbase -= cpu * runtime->save_state_size;
+	staggered_smbase = mp_state.perm_smbase;
+	staggered_smbase -= cpu * runtime->save_state_size;
 
 	printk(BIOS_DEBUG, "New SMBASE 0x%08lx\n", perm_smbase);
 
@@ -747,7 +751,7 @@
 	mp_state.ops.relocation_handler(cpu, curr_smbase, perm_smbase);
 
 	stm_setup(cpu, mp_state.perm_smbase, mp_state.perm_smsize,
-		  perm_smbase, runtime->start32_offset);
+		  staggered_smbase, runtime->start32_offset);
 }
 
 static void adjust_smm_apic_id_map(struct smm_loader_params *smm_params)

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