x86/mm: Fix __swp_entry_to_pte() for Xen PV guests

Normally __swp_entry_to_pte() is never called with a value translating
to a valid PTE. The only known exception is pte_swap_tests(), resulting
in a WARN splat in Xen PV guests, as __pte_to_swp_entry() did
translate the PFN of the valid PTE to a guest local PFN, while
__swp_entry_to_pte() doesn't do the opposite translation.

Fix that by using __pte() in __swp_entry_to_pte() instead of open
coding the native variant of it.

For correctness do the similar conversion for __swp_entry_to_pmd().

Fixes: 05289402 ("mm/debug_vm_pgtable: add tests validating arch helpers for core MM features")
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230306123259.12461-1-jgross@suse.com

arch/x86/include/asm/pgtable_64.h

@@ -237,8 +237,8 @@ static inline void native_pgd_clear(pgd_t *pgd)
 
 #define __pte_to_swp_entry(pte)		((swp_entry_t) { pte_val((pte)) })
 #define __pmd_to_swp_entry(pmd)		((swp_entry_t) { pmd_val((pmd)) })
-#define __swp_entry_to_pte(x)		((pte_t) { .pte = (x).val })
-#define __swp_entry_to_pmd(x)		((pmd_t) { .pmd = (x).val })
+#define __swp_entry_to_pte(x)		(__pte((x).val))
+#define __swp_entry_to_pmd(x)		(__pmd((x).val))
 
 extern void cleanup_highmap(void);