riscv: smp: fail booting up smp if inconsistent vlen is detected

BugLink: https://bugs.launchpad.net/bugs/2083196

[ Upstream commit 38a94c46660f5612c6ef37ec9754ec1543b038cd ]

Currently we only support Vector for SMP platforms, that is, all SMP
cores have the same vlenb. If we happen to detect a mismatching vlen, it
is better to just fail bootting it up to prevent further race/scheduling
issues.

Also, move .Lsecondary_park forward and chage `tail smp_callin` into a
regular call in the early assembly. So a core would be parked right
after a return from smp_callin. Note that a successful smp_callin
does not return.

Fixes: 7017858eb2 ("riscv: Introduce riscv_v_vsize to record size of Vector context")
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Closes: https://lore.kernel.org/linux-riscv/20240228-vicinity-cornstalk-4b8eb5fe5730@spud/
Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Yunhui Cui <cuiyunhui@bytedance.com>
Link: https://lore.kernel.org/r/20240510-zve-detection-v5-2-0711bdd26c12@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>

arch/riscv/kernel/head.S

@@ -165,9 +165,20 @@ secondary_start_sbi:
 #endif
 	call .Lsetup_trap_vector
 	scs_load_current
-	tail smp_callin
+	call smp_callin
 #endif /* CONFIG_SMP */
 
+.align 2
+.Lsecondary_park:
+	/*
+	 * Park this hart if we:
+	 *  - have too many harts on CONFIG_RISCV_BOOT_SPINWAIT
+	 *  - receive an early trap, before setup_trap_vector finished
+	 *  - fail in smp_callin(), as a successful one wouldn't return
+	 */
+	wfi
+	j .Lsecondary_park
+
 .align 2
 .Lsetup_trap_vector:
 	/* Set trap vector to exception handler */
@@ -181,12 +192,6 @@ secondary_start_sbi:
 	csrw CSR_SCRATCH, zero
 	ret
 
-.align 2
-.Lsecondary_park:
-	/* We lack SMP support or have too many harts, so park this hart */
-	wfi
-	j .Lsecondary_park
-
 SYM_CODE_END(_start)
 
 SYM_CODE_START(_start_kernel)

arch/riscv/kernel/smpboot.c

@@ -219,6 +219,15 @@ asmlinkage __visible void smp_callin(void)
 	struct mm_struct *mm = &init_mm;
 	unsigned int curr_cpuid = smp_processor_id();
 
+	if (has_vector()) {
+		/*
+		 * Return as early as possible so the hart with a mismatching
+		 * vlen won't boot.
+		 */
+		if (riscv_v_setup_vsize())
+			return;
+	}
+
 	/* All kernel threads share the same mm context.  */
 	mmgrab(mm);
 	current->active_mm = mm;
@@ -231,11 +240,6 @@ asmlinkage __visible void smp_callin(void)
 	numa_add_cpu(curr_cpuid);
 	set_cpu_online(curr_cpuid, 1);
 
-	if (has_vector()) {
-		if (riscv_v_setup_vsize())
-			elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
-	}
-
 	riscv_user_isa_enable();
 
 	/*