[SRU][J][PATCH 1/1] powerpc/pseries: Fix scv instruction crash with kexec

[Massimiliano Pellizzer]

From: Nicholas Piggin <npiggin at gmail.com>

BugLink: https://bugs.launchpad.net/bugs/2075575

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: 7fa95f9adaee ("powerpc/64s: system call support for scv/rfscv instructions")
Cc: stable at vger.kernel.org # v5.9+
Reported-by: Sourabh Jain <sourabhjain at linux.ibm.com>
Closes: https://lore.kernel.org/3b4b2943-49ad-4619-b195-bc416f1d1409@linux.ibm.com
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
Tested-by: Gautam Menghani <gautam at linux.ibm.com>
Tested-by: Sourabh Jain <sourabhjain at linux.ibm.com>
Link: https://msgid.link/20240625134047.298759-1-npiggin@gmail.com
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
(backported from commit 21a741eb75f80397e5f7d3739e24d7d75e619011)
[mpellizzer: adjusted context due to missing commits:
- e6f6390ab7b9 powerpc: Add missing headers
- cc15ff327569 powerpc/mce: Avoid using irq_work_queue() in realmode
- 2ab2d5794f14 powerpc/kasan: Disable address sanitization in kexec paths
which do not affect the patch.]
Signed-off-by: Massimiliano Pellizzer <massimiliano.pellizzer at canonical.com>
---
 arch/powerpc/kexec/core_64.c           | 11 +++++++++++
 arch/powerpc/platforms/pseries/setup.c | 11 -----------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/kexec/core_64.c b/arch/powerpc/kexec/core_64.c
index 89c069d664a5..09d59628a499 100644
--- a/arch/powerpc/kexec/core_64.c
+++ b/arch/powerpc/kexec/core_64.c
@@ -26,6 +26,7 @@
 #include <asm/mmu.h>
 #include <asm/sections.h>	/* _end */
 #include <asm/prom.h>
+#include <asm/setup.h>
 #include <asm/smp.h>
 #include <asm/hw_breakpoint.h>
 #include <asm/asm-prototypes.h>
@@ -317,6 +318,16 @@ 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.
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 309a72518ecc..95c9d1e38f4b 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -411,16 +411,6 @@ void pseries_disable_reloc_on_exc(void)
 }
 EXPORT_SYMBOL(pseries_disable_reloc_on_exc);
 
-#ifdef CONFIG_KEXEC_CORE
-static void pSeries_machine_kexec(struct kimage *image)
-{
-	if (firmware_has_feature(FW_FEATURE_SET_MODE))
-		pseries_disable_reloc_on_exc();
-
-	default_machine_kexec(image);
-}
-#endif
-
 #ifdef __LITTLE_ENDIAN__
 void pseries_big_endian_exceptions(void)
 {
@@ -1088,7 +1078,6 @@ 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_SPARSE
-- 
2.43.0