linux-kernel - [PATCH] x86/mm: Make pud_present() check _PAGE_PROTNONE and _PAGE

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Message-Id: <1584507679-11976-1-git-send-email-anshuman.khandual@arm.com>
Date:   Wed, 18 Mar 2020 10:31:19 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-mm@...ck.org
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] x86/mm: Make pud_present() check _PAGE_PROTNONE and _PAGE_PSE as well

pud_present() should also check _PAGE_PROTNONE and _PAGE_PSE bits like in
case pmd_present(). This makes a PUD entry test positive for pud_present()
after getting invalidated with pud_mknotpresent(), hence standardizing the
semantics with PMD helpers.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: x86@...nel.org
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
Even though pud_mknotpresent() is not used any where currently, there is
a discrepancy between PMD and PUD.

WARN_ON(!pud_present(pud_mknotpresent(pud_mkhuge(pud)))) -> Fail
WARN_ON(!pmd_present(pmd_mknotpresent(pmd_mkhuge(pmd)))) -> Pass

Though pud_mknotpresent() currently clears _PAGE_PROTNONE, pud_present()
does not check it. This change fixes both inconsistencies.

This has been build and boot tested on x86.

 arch/x86/include/asm/pgtable.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 7e118660bbd9..8adf1d00b506 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -857,7 +857,13 @@ static inline int pud_none(pud_t pud)
 
 static inline int pud_present(pud_t pud)
 {
-	return pud_flags(pud) & _PAGE_PRESENT;
+	/*
+	 * Checking for _PAGE_PSE is needed too because
+	 * split_huge_page will temporarily clear the present bit (but
+	 * the _PAGE_PSE flag will remain set at all times while the
+	 * _PAGE_PRESENT bit is clear).
+	 */
+	return pud_flags(pud) & (_PAGE_PRESENT | _PAGE_PROTNONE | _PAGE_PSE);
 }
 
 static inline unsigned long pud_page_vaddr(pud_t pud)
-- 
2.17.1