linux-kernel - [PATCH v3 1/5] x86/mm: change l1d flush runtime prctl behaviour

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Message-ID: <20201127065938.8200-2-sblbir@amazon.com>
Date:   Fri, 27 Nov 2020 17:59:34 +1100
From:   Balbir Singh <sblbir@...zon.com>
To:     <tglx@...utronix.de>, <mingo@...hat.com>
CC:     <peterz@...radead.org>, <linux-kernel@...r.kernel.org>,
        <keescook@...omium.org>, <jpoimboe@...hat.com>,
        <tony.luck@...el.com>, <benh@...nel.crashing.org>,
        <x86@...nel.org>, <dave.hansen@...el.com>,
        <thomas.lendacky@....com>, <torvalds@...ux-foundation.org>,
        Balbir Singh <sblbir@...zon.com>
Subject: [PATCH v3 1/5] x86/mm: change l1d flush runtime prctl behaviour

Detection of task affinities at API opt-in time is not the best
approach, the approach is to kill the task if it runs on a
SMT enable core. This is better than not flushing the L1D cache
when the task switches from a non-SMT core to an SMT enabled core.

Signed-off-by: Balbir Singh <sblbir@...zon.com>
---
 arch/x86/include/asm/processor.h |  2 ++
 arch/x86/kernel/smpboot.c        | 11 ++++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 82a08b585818..60dbcdcb833f 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -136,6 +136,8 @@ struct cpuinfo_x86 {
 	u16			logical_die_id;
 	/* Index into per_cpu list: */
 	u16			cpu_index;
+	/*  Is SMT active on this core? */
+	bool			smt_active;
 	u32			microcode;
 	/* Address space bits used by the cache internally */
 	u8			x86_cache_bits;
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index de776b2e6046..9a94934fae5f 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -635,6 +635,9 @@ void set_cpu_sibling_map(int cpu)
 	threads = cpumask_weight(topology_sibling_cpumask(cpu));
 	if (threads > __max_smt_threads)
 		__max_smt_threads = threads;
+
+	for_each_cpu(i, topology_sibling_cpumask(cpu))
+		cpu_data(i).smt_active = threads > 1;
 }
 
 /* maps the cpu to the sched domain representing multi-core */
@@ -1548,10 +1551,16 @@ static void remove_siblinginfo(int cpu)
 
 	for_each_cpu(sibling, topology_die_cpumask(cpu))
 		cpumask_clear_cpu(cpu, topology_die_cpumask(sibling));
-	for_each_cpu(sibling, topology_sibling_cpumask(cpu))
+
+	for_each_cpu(sibling, topology_sibling_cpumask(cpu)) {
 		cpumask_clear_cpu(cpu, topology_sibling_cpumask(sibling));
+		if (cpumask_weight(topology_sibling_cpumask(sibling)) == 1)
+			cpu_data(sibling).smt_active = false;
+	}
+
 	for_each_cpu(sibling, cpu_llc_shared_mask(cpu))
 		cpumask_clear_cpu(cpu, cpu_llc_shared_mask(sibling));
+
 	cpumask_clear(cpu_llc_shared_mask(cpu));
 	cpumask_clear(topology_sibling_cpumask(cpu));
 	cpumask_clear(topology_core_cpumask(cpu));
-- 
2.17.1