powerpc/pseries: Fix scv instruction crash with kexec

JIRA: https://issues.redhat.com/browse/RHEL-14159

commit 21a741e
Author: Nicholas Piggin <npiggin@gmail.com>
Date:   Tue Jun 25 23:40:47 2024 +1000

    powerpc/pseries: Fix scv instruction crash with kexec

    kexec on pseries disables AIL (reloc_on_exc), required for scv
    instruction support, before other CPUs have been shut down. This means
    they can execute scv instructions after AIL is disabled, which causes an
    interrupt at an unexpected entry location that crashes the kernel.

    Change the kexec sequence to disable AIL after other CPUs have been
    brought down.

    As a refresher, the real-mode scv interrupt vector is 0x17000, and the
    fixed-location head code probably couldn't easily deal with implementing
    such high addresses so it was just decided not to support that interrupt
    at all.

    Fixes: 7fa95f9 ("powerpc/64s: system call support for scv/rfscv instructions")
    Cc: stable@vger.kernel.org # v5.9+
    Reported-by: Sourabh Jain <sourabhjain@linux.ibm.com>
    Closes: https://lore.kernel.org/3b4b2943-49ad-4619-b195-bc416f1d1409@linux.ibm.com
    Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
    Tested-by: Gautam Menghani <gautam@linux.ibm.com>
    Tested-by: Sourabh Jain <sourabhjain@linux.ibm.com>
    Link: https://msgid.link/20240625134047.298759-1-npiggin@gmail.com
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Author: Mamatha Inamdar

arch/powerpc/kexec/core_64.c

@@ -26,6 +26,7 @@
 #include <asm/paca.h>
 #include <asm/mmu.h>
 #include <asm/sections.h>	/* _end */
+#include <asm/setup.h>
 #include <asm/smp.h>
 #include <asm/hw_breakpoint.h>
 #include <asm/asm-prototypes.h>
@@ -315,6 +316,16 @@ void default_machine_kexec(struct kimage *image)
 	if (!kdump_in_progress())
 		kexec_prepare_cpus();
 
+#ifdef CONFIG_PPC_PSERIES
+	/* This must be done after other CPUs have shut down, otherwise they
+	 * could execute the 'scv' instruction, which is not supported with
+	 * reloc disabled (see configure_exceptions()).
+	 */
+	
+	if (firmware_has_feature(FW_FEATURE_SET_MODE))
+		pseries_disable_reloc_on_exc();
+#endif
+	
 	printk("kexec: Starting switchover sequence.\n");
 
 	/* switch to a staticly allocated stack.  Based on irq stack code.

arch/powerpc/platforms/pseries/kexec.c

@@ -61,11 +61,3 @@ void pseries_kexec_cpu_down(int crash_shutdown, int secondary)
 	} else
 		xics_kexec_teardown_cpu(secondary);
 }
-
-void pseries_machine_kexec(struct kimage *image)
-{
-	if (firmware_has_feature(FW_FEATURE_SET_MODE))
-		pseries_disable_reloc_on_exc();
-
-	default_machine_kexec(image);
-}

arch/powerpc/platforms/pseries/pseries.h

@@ -37,7 +37,6 @@ static inline void smp_init_pseries(void) { }
 #endif
 
 extern void pseries_kexec_cpu_down(int crash_shutdown, int secondary);
-void pseries_machine_kexec(struct kimage *image);
 
 extern void pSeries_final_fixup(void);
 

arch/powerpc/platforms/pseries/setup.c

@@ -1093,7 +1093,6 @@ define_machine(pseries) {
 	.machine_check_early	= pseries_machine_check_realmode,
 	.machine_check_exception = pSeries_machine_check_exception,
 #ifdef CONFIG_KEXEC_CORE
-	.machine_kexec          = pseries_machine_kexec,
 	.kexec_cpu_down         = pseries_kexec_cpu_down,
 #endif
 #ifdef CONFIG_MEMORY_HOTPLUG