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

[Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>]

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_exception().

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_exception().

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@xxxxxxxxxxxxxxx # 6.6+
Fixes: af19487f00f3 ("mm: make PTE_MARKER_SWAPIN_ERROR more general")
Reported-by: Yunseong Kim <yskelg@xxxxxxxxx>
Tested-by: Yunseong Kim <yskelg@xxxxxxxxx>
Acked-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Signed-off-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
Message-ID: <20240715180416.3632453-1-gerald.schaefer@xxxxxxxxxxxxx>
Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 6b19a33c49c2..8e149ef5e89b 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -433,12 +433,13 @@ static void do_exception(struct pt_regs *regs, int access)
 			handle_fault_error_nolock(regs, 0);
 		else
 			do_sigsegv(regs, SEGV_MAPERR);
-	} else if (fault & VM_FAULT_SIGBUS) {
+	} else if (fault & (VM_FAULT_SIGBUS | VM_FAULT_HWPOISON)) {
 		if (!user_mode(regs))
 			handle_fault_error_nolock(regs, 0);
 		else
 			do_sigbus(regs);
 	} else {
+		pr_emerg("Unexpected fault flags: %08x\n", fault);
 		BUG();
 	}
 }