Subject: [kvm-unit-tests PATCH v9 14/31] powerpc: Remove broken SMP exception stack setup

From: Nicholas Piggin <[email-masked]>
Date: Sat, 4 May 2024 22:28:20 +1000

The exception stack setup does not work correctly for SMP, because
it is the boot processor that calls cpu_set() which sets SPRG2 to
the exception stack, not the target CPU itself. So secondaries
never got their SPRG2 set to a valid exception stack.

Remove the SMP code and just set an exception stack for the boot
processor. Make the stack 64kB while we're here, to match the
size of the regular stack.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 lib/powerpc/setup.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/lib/powerpc/setup.c b/lib/powerpc/setup.c
index 9b665f59c..58be93f08 100644
--- a/lib/powerpc/setup.c
+++ b/lib/powerpc/setup.c
@@ -42,10 +42,6 @@ struct cpu_set_params {
 	uint64_t tb_hz;
 };
 
-#define EXCEPTION_STACK_SIZE	(32*1024) /* 32kB */
-
-static char exception_stack[NR_CPUS][EXCEPTION_STACK_SIZE];
-
 static void cpu_set(int fdtnode, u64 regval, void *info)
 {
 	static bool read_common_info = false;
@@ -56,10 +52,6 @@ static void cpu_set(int fdtnode, u64 regval, void *info)
 
 	cpus[cpu] = regval;
 
-	/* set exception stack address for this CPU (in SPGR0) */
-	asm volatile ("mtsprg0 %[addr]" ::
-		      [addr] "r" (exception_stack[cpu + 1]));
-
 	if (!read_common_info) {
 		const struct fdt_property *prop;
 		u32 *data;
@@ -180,6 +172,10 @@ static void mem_init(phys_addr_t freemem_start)
 					 ? __icache_bytes : __dcache_bytes);
 }
 
+#define EXCEPTION_STACK_SIZE	SZ_64K
+
+static char boot_exception_stack[EXCEPTION_STACK_SIZE];
+
 void setup(const void *fdt)
 {
 	void *freemem = &stacktop;
@@ -189,6 +185,10 @@ void setup(const void *fdt)
 
 	cpu_has_hv = !!(mfmsr() & (1ULL << MSR_HV_BIT));
 
+	/* set exception stack address for this CPU (in SPGR0) */
+	asm volatile ("mtsprg0 %[addr]" ::
+		      [addr] "r" (boot_exception_stack + EXCEPTION_STACK_SIZE - 64));
+
 	enable_mcheck();
 
 	/*
-- 
2.43.0