[PATCH] s390/mm: Fix VM_FAULT_HWPOISON handling in do_fault_error()

[Yunseong Kim <yskelg@gmail.com>]

This patch backporting to v6.6.43+ cherry picked from
commit df39038cd895 ("s390/mm: Fix VM_FAULT_HWPOISON handling in do_exception()")

There is no support for HWPOISON, MEMORY_FAILURE, or ARCH_HAS_COPY_MC on
s390. Therefore we do not expect to see VM_FAULT_HWPOISON in
do_fault_error().

However, since commit af19487f00f3 ("mm: make PTE_MARKER_SWAPIN_ERROR more
general"), it is possible to see VM_FAULT_HWPOISON in combination with
PTE_MARKER_POISONED, even on architectures that do not support HWPOISON
otherwise. In this case, we will end up on the BUG() in do_fault_error().

Fix this by treating VM_FAULT_HWPOISON the same as VM_FAULT_SIGBUS, similar
to x86 when MEMORY_FAILURE is not configured. Also print unexpected fault
flags, for easier debugging.

Note that VM_FAULT_HWPOISON_LARGE is not expected, because s390 cannot
support swap entries on other levels than PTE level.

Cc: stable@vger.kernel.org # 6.6+
Fixes: af19487f00f3 ("mm: make PTE_MARKER_SWAPIN_ERROR more general")
Reported-by: Yunseong Kim <yskelg@gmail.com>
Tested-by: Yunseong Kim <yskelg@gmail.com>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Message-ID: <20240715180416.3632453-1-gerald.schaefer@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Yunseong Kim <yskelg@gmail.com>
---
 arch/s390/mm/fault.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index b678295931c3..1a231181a413 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -331,14 +331,16 @@ static noinline void do_fault_error(struct pt_regs *regs, vm_fault_t fault)
 				do_no_context(regs, fault);
 			else
 				do_sigsegv(regs, SEGV_MAPERR);
-		} else if (fault & VM_FAULT_SIGBUS) {
+		} else if (fault & (VM_FAULT_SIGBUS | VM_FAULT_HWPOISON)) {
 			/* Kernel mode? Handle exceptions or die */
 			if (!user_mode(regs))
 				do_no_context(regs, fault);
 			else
 				do_sigbus(regs);
-		} else
+		} else {
+			pr_emerg("Unexpected fault flags: %08x\n", fault);
 			BUG();
+		}
 		break;
 	}
 }
-- 
2.45.2