[tip:x86/pti] x86/mm: Remove extra filtering in pageattr code

[tip-bot for Dave Hansen]

Commit-ID:  1a54420aeb4da1ba5b28283aa5696898220c9a27
Gitweb:     https://git.kernel.org/tip/1a54420aeb4da1ba5b28283aa5696898220c9a27
Author:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
AuthorDate: Fri, 6 Apr 2018 13:55:11 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 12 Apr 2018 09:05:58 +0200

x86/mm: Remove extra filtering in pageattr code

The pageattr code has a mode where it can set or clear PTE bits in
existing PTEs, so the page protections of the *new* PTEs come from
one of two places:

  1. The set/clear masks: cpa->mask_clr / cpa->mask_set
  2. The existing PTE

We filter ->mask_set/clr for supported PTE bits at entry to
__change_page_attr() so we never need to filter them again.

The only other place permissions can come from is an existing PTE
and those already presumably have good bits.  We do not need to filter
them again.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Nadav Amit <namit@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Link: http://lkml.kernel.org/r/20180406205511.BC072352@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/mm/pageattr.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index d3442dfdfced..968f51a2e39b 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -598,7 +598,6 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
 	req_prot = pgprot_clear_protnone_bits(req_prot);
 	if (pgprot_val(req_prot) & _PAGE_PRESENT)
 		pgprot_val(req_prot) |= _PAGE_PSE;
-	req_prot = canon_pgprot(req_prot);
 
 	/*
 	 * old_pfn points to the large page base pfn. So we need
@@ -718,7 +717,7 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 	 */
 	pfn = ref_pfn;
 	for (i = 0; i < PTRS_PER_PTE; i++, pfn += pfninc)
-		set_pte(&pbase[i], pfn_pte(pfn, canon_pgprot(ref_prot)));
+		set_pte(&pbase[i], pfn_pte(pfn, ref_prot));
 
 	if (virt_addr_valid(address)) {
 		unsigned long pfn = PFN_DOWN(__pa(address));
@@ -935,7 +934,6 @@ static void populate_pte(struct cpa_data *cpa,
 	pte = pte_offset_kernel(pmd, start);
 
 	pgprot = pgprot_clear_protnone_bits(pgprot);
-	pgprot = canon_pgprot(pgprot);
 
 	while (num_pages-- && start < end) {
 		set_pte(pte, pfn_pte(cpa->pfn, pgprot));
@@ -1234,7 +1232,7 @@ repeat:
 		 * after all we're only going to change it's attributes
 		 * not the memory it points to
 		 */
-		new_pte = pfn_pte(pfn, canon_pgprot(new_prot));
+		new_pte = pfn_pte(pfn, new_prot);
 		cpa->pfn = pfn;
 		/*
 		 * Do we really change anything ?