linux-kernel - [tip:x86/mm] generic/pgtable: Introduce set_pte

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Date:   Wed, 5 Dec 2018 10:06:11 -0800
From:   tip-bot for Dan Williams <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     riel@...riel.com, dave.hansen@...ux.intel.com,
        linux-kernel@...r.kernel.org, hpa@...or.com,
        kirill.shutemov@...ux.intel.com, luto@...nel.org,
        dave.hansen@...el.com, bigeasy@...utronix.de,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        dan.j.williams@...el.com, bp@...en8.de, mingo@...nel.org,
        peterz@...radead.org
Subject: [tip:x86/mm] generic/pgtable: Introduce set_pte_safe()

Commit-ID:  4369deaa2f022ef92da45a0e7eec8a4a52e8e8a4
Gitweb:     https://git.kernel.org/tip/4369deaa2f022ef92da45a0e7eec8a4a52e8e8a4
Author:     Dan Williams <dan.j.williams@...el.com>
AuthorDate: Tue, 4 Dec 2018 13:37:16 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 5 Dec 2018 09:03:06 +0100

generic/pgtable: Introduce set_pte_safe()

Commit:

  f77084d96355 "x86/mm/pat: Disable preemption around __flush_tlb_all()"

introduced a warning to capture cases __flush_tlb_all() is called without
pre-emption disabled. It triggers a false positive warning in the memory
hotplug path.

On investigation it was found that the __flush_tlb_all() calls are not
necessary. However, they are only "not necessary" in practice provided
the ptes are being initially populated from the !present state.

Introduce set_pte_safe() as a sanity check that the pte is being updated
in a way that does not require a TLB flush.

Forgive the macro, the availability of the various of set_pte() levels
is hit and miss across architectures.

[ mingo: Minor readability edits. ]

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Suggested-by: Dave Hansen <dave.hansen@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Rik van Riel <riel@...riel.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: https://lkml.kernel.org/r/279dadae-9148-465c-7ec6-3f37e026c6c9@intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/asm-generic/pgtable.h | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index dae7f98babed..a9cac82e9a7a 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -400,6 +400,44 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
 }
 #endif
 
+/*
+ * Use set_p*_safe(), and elide TLB flushing, when confident that *no*
+ * TLB flush will be required as a result of the "set". For example, use
+ * in scenarios where it is known ahead of time that the routine is
+ * setting non-present entries, or re-setting an existing entry to the
+ * same value. Otherwise, use the typical "set" helpers and flush the
+ * TLB.
+ */
+#define set_pte_safe(ptep, pte) \
+({ \
+	WARN_ON_ONCE(pte_present(*ptep) && !pte_same(*ptep, pte)); \
+	set_pte(ptep, pte); \
+})
+
+#define set_pmd_safe(pmdp, pmd) \
+({ \
+	WARN_ON_ONCE(pmd_present(*pmdp) && !pmd_same(*pmdp, pmd)); \
+	set_pmd(pmdp, pmd); \
+})
+
+#define set_pud_safe(pudp, pud) \
+({ \
+	WARN_ON_ONCE(pud_present(*pudp) && !pud_same(*pudp, pud)); \
+	set_pud(pudp, pud); \
+})
+
+#define set_p4d_safe(p4dp, p4d) \
+({ \
+	WARN_ON_ONCE(p4d_present(*p4dp) && !p4d_same(*p4dp, p4d)); \
+	set_p4d(p4dp, p4d); \
+})
+
+#define set_pgd_safe(pgdp, pgd) \
+({ \
+	WARN_ON_ONCE(pgd_present(*pgdp) && !pgd_same(*pgdp, pgd)); \
+	set_pgd(pgdp, pgd); \
+})
+
 #ifndef __HAVE_ARCH_DO_SWAP_PAGE
 /*
  * Some architectures support metadata associated with a page. When a