[PATCH 6.1 150/181] powerpc/64s: Fix __pte_needs_flush() false positive warning

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From: Benjamin Gray <bgray@xxxxxxxxxxxxx>

commit 1abce0580b89464546ae06abd5891ebec43c9470 upstream.

Userspace PROT_NONE ptes set _PAGE_PRIVILEGED, triggering a false
positive debug assertion that __pte_flags_need_flush() is not called
on a kernel mapping.

Detect when it is a userspace PROT_NONE page by checking the required
bits of PAGE_NONE are set, and none of the RWX bits are set.
pte_protnone() is insufficient here because it always returns 0 when
CONFIG_NUMA_BALANCING=n.

Fixes: b11931e9adc1 ("powerpc/64s: add pte_needs_flush and huge_pmd_needs_flush")
Cc: stable@xxxxxxxxxxxxxxx # v6.1+
Reported-by: Russell Currey <ruscur@xxxxxxxxxx>
Signed-off-by: Benjamin Gray <bgray@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://msgid.link/20230302225947.81083-1-bgray@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/include/asm/book3s/64/tlbflush.h |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/arch/powerpc/include/asm/book3s/64/tlbflush.h
+++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h
@@ -163,6 +163,11 @@ static inline void flush_tlb_fix_spuriou
 	 */
 }
 
+static inline bool __pte_protnone(unsigned long pte)
+{
+	return (pte & (pgprot_val(PAGE_NONE) | _PAGE_RWX)) == pgprot_val(PAGE_NONE);
+}
+
 static inline bool __pte_flags_need_flush(unsigned long oldval,
 					  unsigned long newval)
 {
@@ -179,8 +184,8 @@ static inline bool __pte_flags_need_flus
 	/*
 	 * We do not expect kernel mappings or non-PTEs or not-present PTEs.
 	 */
-	VM_WARN_ON_ONCE(oldval & _PAGE_PRIVILEGED);
-	VM_WARN_ON_ONCE(newval & _PAGE_PRIVILEGED);
+	VM_WARN_ON_ONCE(!__pte_protnone(oldval) && oldval & _PAGE_PRIVILEGED);
+	VM_WARN_ON_ONCE(!__pte_protnone(newval) && newval & _PAGE_PRIVILEGED);
 	VM_WARN_ON_ONCE(!(oldval & _PAGE_PTE));
 	VM_WARN_ON_ONCE(!(newval & _PAGE_PTE));
 	VM_WARN_ON_ONCE(!(oldval & _PAGE_PRESENT));





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