linux-kernel - [tip:x86/pti] x86/mm: Undo double _PAGE

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Message-ID: <tip-606c7193d5fbf8ea3dafc8a9468f719fbf1d7160@git.kernel.org>
Date:   Mon, 9 Apr 2018 10:12:21 -0700
From:   tip-bot for Dave Hansen <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     jgross@...e.com, peterz@...radead.org, gregkh@...uxfoundation.org,
        namit@...are.com, hughd@...gle.com, torvalds@...ux-foundation.org,
        tglx@...utronix.de, keescook@...gle.com, dan.j.williams@...el.com,
        arjan@...ux.intel.com, jpoimboe@...hat.com, bp@...en8.de,
        mingo@...nel.org, aarcange@...hat.com, dave.hansen@...ux.intel.com,
        linux-kernel@...r.kernel.org, dwmw2@...radead.org, luto@...nel.org,
        hpa@...or.com
Subject: [tip:x86/pti] x86/mm: Undo double _PAGE_PSE clearing

Commit-ID:  606c7193d5fbf8ea3dafc8a9468f719fbf1d7160
Gitweb:     https://git.kernel.org/tip/606c7193d5fbf8ea3dafc8a9468f719fbf1d7160
Author:     Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate: Fri, 6 Apr 2018 13:55:04 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 9 Apr 2018 18:27:32 +0200

x86/mm: Undo double _PAGE_PSE clearing

When clearing _PAGE_PRESENT on a huge page, we need to be careful
to also clear _PAGE_PSE, otherwise it might still get confused
for a valid large page table entry.

We do that near the spot where we *set* _PAGE_PSE.  That's fine,
but it's unnecessary.  pgprot_large_2_4k() already did it.

BTW, I also noticed that pgprot_large_2_4k() and
pgprot_4k_2_large() are not symmetric.  pgprot_large_2_4k() clears
_PAGE_PSE (because it is aliased to _PAGE_PAT) but
pgprot_4k_2_large() does not put _PAGE_PSE back.  Bummer.

Also, add some comments and change "promote" to "move".  "Promote"
seems an odd word to move when we are logically moving a bit to a
lower bit position.  Also add an extra line return to make it clear
to which line the comment applies.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Kees Cook <keescook@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Nadav Amit <namit@...are.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-mm@...ck.org
Link: http://lkml.kernel.org/r/20180406205504.9B0F44A9@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/mm/pageattr.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 4d369d5c04c5..d3442dfdfced 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -583,6 +583,7 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
 	 * up accordingly.
 	 */
 	old_pte = *kpte;
+	/* Clear PSE (aka _PAGE_PAT) and move PAT bit to correct position */
 	req_prot = pgprot_large_2_4k(old_prot);
 
 	pgprot_val(req_prot) &= ~pgprot_val(cpa->mask_clr);
@@ -597,8 +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;
-	else
-		pgprot_val(req_prot) &= ~_PAGE_PSE;
 	req_prot = canon_pgprot(req_prot);
 
 	/*
@@ -684,8 +683,12 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 	switch (level) {
 	case PG_LEVEL_2M:
 		ref_prot = pmd_pgprot(*(pmd_t *)kpte);
-		/* clear PSE and promote PAT bit to correct position */
+		/*
+		 * Clear PSE (aka _PAGE_PAT) and move
+		 * PAT bit to correct position.
+		 */
 		ref_prot = pgprot_large_2_4k(ref_prot);
+
 		ref_pfn = pmd_pfn(*(pmd_t *)kpte);
 		break;