arm64: Fix pte_modify() to preserve the hardware dirty information

The pte_modify() function with hardware AF/DBM enabled must transfer the
hardware dirty information to the software PTE_DIRTY bit. However, it
was setting this bit in newprot and the mask does not cover such bit.
This patch sets PTE_DIRTY on the original pte which will be preserved in
the returned value.

Fixes: 2f4b829c625e ("arm64: Add support for hardware updates of the access and dirty pte bits")
Cc: Julien Grall <julien.grall@citrix.com>
Tested-by: Julien Grall <julien.grall@citrix.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/pgtable.h

@@ -503,7 +503,7 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 			      PTE_PROT_NONE | PTE_WRITE | PTE_TYPE_MASK;
 	/* preserve the hardware dirty information */
 	if (pte_hw_dirty(pte))
-		newprot |= PTE_DIRTY;
+		pte = pte_mkdirty(pte);
 	pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
 	return pte;
 }