linux-kernel - [tip:x86/mm] x86/mm: Delete a big outdated comment about TLB flushing

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Date:   Fri, 30 Jun 2017 06:11:46 -0700
From:   tip-bot for Andy Lutomirski <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     dave.hansen@...el.com, bp@...en8.de, arjan@...ux.intel.com,
        linux-kernel@...r.kernel.org, nadav.amit@...il.com, hpa@...or.com,
        luto@...nel.org, tglx@...utronix.de, mingo@...nel.org,
        akpm@...ux-foundation.org, riel@...hat.com,
        torvalds@...ux-foundation.org, mgorman@...e.de,
        peterz@...radead.org
Subject: [tip:x86/mm] x86/mm: Delete a big outdated comment about TLB
 flushing

Commit-ID:  8781fb7e9749da424e01daacd14834b674658c63
Gitweb:     http://git.kernel.org/tip/8781fb7e9749da424e01daacd14834b674658c63
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Thu, 29 Jun 2017 08:53:14 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 30 Jun 2017 10:12:35 +0200

x86/mm: Delete a big outdated comment about TLB flushing

The comment describes the old explicit IPI-based flush logic, which
is long gone.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Nadav Amit <nadav.amit@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-mm@...ck.org
Link: http://lkml.kernel.org/r/55e44997e56086528140c5180f8337dc53fb7ffc.1498751203.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/mm/tlb.c | 36 ------------------------------------
 1 file changed, 36 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 1cc4783..014d07a 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -153,42 +153,6 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
 	switch_ldt(real_prev, next);
 }
 
-/*
- * The flush IPI assumes that a thread switch happens in this order:
- * [cpu0: the cpu that switches]
- * 1) switch_mm() either 1a) or 1b)
- * 1a) thread switch to a different mm
- * 1a1) set cpu_tlbstate to TLBSTATE_OK
- *	Now the tlb flush NMI handler flush_tlb_func won't call leave_mm
- *	if cpu0 was in lazy tlb mode.
- * 1a2) update cpu active_mm
- *	Now cpu0 accepts tlb flushes for the new mm.
- * 1a3) cpu_set(cpu, new_mm->cpu_vm_mask);
- *	Now the other cpus will send tlb flush ipis.
- * 1a4) change cr3.
- * 1a5) cpu_clear(cpu, old_mm->cpu_vm_mask);
- *	Stop ipi delivery for the old mm. This is not synchronized with
- *	the other cpus, but flush_tlb_func ignore flush ipis for the wrong
- *	mm, and in the worst case we perform a superfluous tlb flush.
- * 1b) thread switch without mm change
- *	cpu active_mm is correct, cpu0 already handles flush ipis.
- * 1b1) set cpu_tlbstate to TLBSTATE_OK
- * 1b2) test_and_set the cpu bit in cpu_vm_mask.
- *	Atomically set the bit [other cpus will start sending flush ipis],
- *	and test the bit.
- * 1b3) if the bit was 0: leave_mm was called, flush the tlb.
- * 2) switch %%esp, ie current
- *
- * The interrupt must handle 2 special cases:
- * - cr3 is changed before %%esp, ie. it cannot use current->{active_,}mm.
- * - the cpu performs speculative tlb reads, i.e. even if the cpu only
- *   runs in kernel space, the cpu could load tlb entries for user space
- *   pages.
- *
- * The good news is that cpu_tlbstate is local to each cpu, no
- * write/read ordering problems.
- */
-
 static void flush_tlb_func_common(const struct flush_tlb_info *f,
 				  bool local, enum tlb_flush_reason reason)
 {