[RFC 2/2] x86/mm/cpa: drop pgprot_clear_protnone_bits()

[Hyeonggon Yoo <42.hyeyoo@gmail.com>]

commit a8aed3e0752b4 ("x86/mm/pageattr: Prevent PSE and GLOABL leftovers
to confuse pmd/pte_present and pmd_huge") made CPA clear _PAGE_GLOBAL when
_PAGE_PRESENT is not set. This prevents kernel crashing when kernel reads
a page with !_PAGE_PRESENT and _PAGE_PROTNONE (_PAGE_GLOBAL). And then it
set _PAGE_GLOBAL back when setting _PAGE_PRESENT again.

After commit d1440b23c922d ("x86/mm: Factor out pageattr _PAGE_GLOBAL
setting") made kernel not set unconditionally _PAGE_GLOBAL, pages lose
global flag after _set_pages_np() and _set_pages_p() are called.

But after commit 3166851142411 ("x86: skip check for spurious faults for
non-present faults"), spurious_kernel_fault() does not confuse
pte/pmd entries with _PAGE_PROTNONE as present anymore. So simply
drop pgprot_clear_protnone_bits().

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
---
 arch/x86/mm/pat/set_memory.c | 24 ------------------------
 1 file changed, 24 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 67cf969fed0d..8a8ce8d78694 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -746,23 +746,6 @@ static void __set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
 #endif
 }
 
-static pgprot_t pgprot_clear_protnone_bits(pgprot_t prot)
-{
-	/*
-	 * _PAGE_GLOBAL means "global page" for present PTEs.
-	 * But, it is also used to indicate _PAGE_PROTNONE
-	 * for non-present PTEs.
-	 *
-	 * This ensures that a _PAGE_GLOBAL PTE going from
-	 * present to non-present is not confused as
-	 * _PAGE_PROTNONE.
-	 */
-	if (!(pgprot_val(prot) & _PAGE_PRESENT))
-		pgprot_val(prot) &= ~_PAGE_GLOBAL;
-
-	return prot;
-}
-
 static int __should_split_large_page(pte_t *kpte, unsigned long address,
 				     struct cpa_data *cpa)
 {
@@ -824,7 +807,6 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
 	 * different bit positions in the two formats.
 	 */
 	req_prot = pgprot_4k_2_large(req_prot);
-	req_prot = pgprot_clear_protnone_bits(req_prot);
 	if (pgprot_val(req_prot) & _PAGE_PRESENT)
 		pgprot_val(req_prot) |= _PAGE_PSE;
 
@@ -1013,8 +995,6 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 		return 1;
 	}
 
-	ref_prot = pgprot_clear_protnone_bits(ref_prot);
-
 	/*
 	 * Get the target pfn from the original entry:
 	 */
@@ -1246,8 +1226,6 @@ static void populate_pte(struct cpa_data *cpa,
 
 	pte = pte_offset_kernel(pmd, start);
 
-	pgprot = pgprot_clear_protnone_bits(pgprot);
-
 	while (num_pages-- && start < end) {
 		set_pte(pte, pfn_pte(cpa->pfn, pgprot));
 
@@ -1542,8 +1520,6 @@ static int __change_page_attr(struct cpa_data *cpa, int primary)
 		new_prot = static_protections(new_prot, address, pfn, 1, 0,
 					      CPA_PROTECT);
 
-		new_prot = pgprot_clear_protnone_bits(new_prot);
-
 		/*
 		 * We need to keep the pfn from the existing PTE,
 		 * after all we're only going to change it's attributes
-- 
2.32.0