linux-kernel - [PATCH 10/11] x86,tlb: really leave mm on shootdown

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Date:   Wed,  1 Aug 2018 06:02:54 -0400
From:   Rik van Riel <riel@...riel.com>
To:     linux-kernel@...r.kernel.org
Cc:     kernel-team@...com, mingo@...nel.org, peterz@...radead.org,
        luto@...nel.org, x86@...nel.org, efault@....de,
        dave.hansen@...el.com, Rik van Riel <riel@...riel.com>
Subject: [PATCH 10/11] x86,tlb: really leave mm on shootdown

When getting an mm shot down from under us in lazy TLB mode, don't
just switch the TLB over to the init_mm page tables, but really drop
our references to the lazy TLB mm.

This allows for faster (instant) freeing of a lazy TLB mm, which is
a precondition to getting rid of the refcounting of mms in lazy TLB mode.

Signed-off-by: Rik van Riel <riel@...riel.com>
---
 arch/x86/mm/tlb.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 7b1add904396..425cb9fa2640 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -140,6 +140,8 @@ void leave_mm(void *dummy)
 	WARN_ON(!this_cpu_read(cpu_tlbstate.is_lazy));
 
 	switch_mm(NULL, &init_mm, NULL);
+	current->active_mm = &init_mm;
+	mmdrop(loaded_mm);
 }
 EXPORT_SYMBOL_GPL(leave_mm);
 
@@ -483,6 +485,8 @@ static void flush_tlb_func_common(const struct flush_tlb_info *f,
 		 * IPIs to lazy TLB mode CPUs.
 		 */
 		switch_mm_irqs_off(NULL, &init_mm, NULL);
+		current->active_mm = &init_mm;
+		mmdrop(loaded_mm);
 		return;
 	}
 
-- 
2.14.4