s390/mm: Fix VM_FAULT_HWPOISON handling in do_exception()

JIRA: https://issues.redhat.com/browse/RHEL-74362
Tested: by me
Conflicts: due b20c821 patchset not being backported

commit df39038
Author: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Date:   Mon Jul 15 20:04:16 2024 +0200

    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_exception().

    However, since commit af19487 ("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@vger.kernel.org # 6.6+
    Fixes: af19487 ("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: Aristeu Rozanski <arozansk@redhat.com>

Author: aristeu

arch/s390/mm/fault.c

@@ -307,13 +307,14 @@ static void do_fault_error(struct pt_regs *regs, vm_fault_t fault)
 				do_no_context(regs);
 			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);
 			else
 				do_sigbus(regs);
 		} else {
+			pr_emerg("Unexpected fault flags: %08x\n", fault);
 			BUG();
 		}
 		break;