linux-kernel - [RFT PATCH v2 4/4] arm64: reuse FPSIMD hardware context if possible

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1381674029-430-4-git-send-email-liuj97@gmail.com>
Date:	Sun, 13 Oct 2013 22:20:20 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Jiang Liu <jiang.liu@...wei.com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Javi Merino <javi.merino@....com>,
	Marc Zyngier <marc.zyngier@....com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:	Jiang Liu <liuj97@...il.com>
Subject: [RFT PATCH v2 4/4] arm64: reuse FPSIMD hardware context if possible

From: Jiang Liu <jiang.liu@...wei.com>

Reuse FPSIMD hardware context if it hasn't been touched by other thread
yet, so we can get rid of unnecessary FPSIMD context restores. This is
especially useful when switching between kernel thread and user thread
because kernel thread usaually doesn't touch FPSIMD registers.

Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
Cc: Jiang Liu <liuj97@...il.com>
---
 arch/arm64/include/asm/fpsimd.h |  2 ++
 arch/arm64/kernel/fpsimd.c      | 35 +++++++++++++++++++++++++++++++++--
 arch/arm64/kernel/smp.c         |  1 +
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
index 6f034082f..ab7bf61 100644
--- a/arch/arm64/include/asm/fpsimd.h
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -35,6 +35,7 @@ struct fpsimd_state {
 			__uint128_t vregs[32];
 			u32 fpsr;
 			u32 fpcr;
+			int last_cpu;
 		};
 	};
 };
@@ -56,6 +57,7 @@ struct task_struct;
 
 extern void fpsimd_save_state(struct fpsimd_state *state);
 extern void fpsimd_load_state(struct fpsimd_state *state);
+extern void fpsimd_reset_lazy_restore(void);
 
 extern void fpsimd_dup_task_struct(struct task_struct *dst,
 				   struct task_struct *src);
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 604fe9f..b1b3b0e 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -22,6 +22,7 @@
 #include <linux/sched.h>
 #include <linux/signal.h>
 #include <linux/hardirq.h>
+#include <linux/percpu.h>
 
 #include <asm/fpsimd.h>
 #include <asm/cputype.h>
@@ -33,6 +34,13 @@
 #define FPEXC_IXF	(1 << 4)
 #define FPEXC_IDF	(1 << 7)
 
+static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_owner);
+
+static inline void fpsimd_set_last_cpu(struct fpsimd_state *state, int cpu)
+{
+	state->last_cpu = cpu;
+}
+
 static inline void fpsimd_init_hw_state(void)
 {
 	int val = AARCH64_FPCR_DEFAULT_VAL;
@@ -83,19 +91,41 @@ void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
 	send_sig_info(SIGFPE, &info, current);
 }
 
+static void fpsimd_load_state_lazy(struct fpsimd_state *state)
+{
+	/* Could we reuse the hardware context? */
+	if (state->last_cpu == smp_processor_id() &&
+	    __this_cpu_read(fpsimd_owner) == state)
+		return;
+	fpsimd_load_state(state);
+}
+
+static void fpsimd_save_state_lazy(struct fpsimd_state *state)
+{
+	fpsimd_save_state(state);
+	fpsimd_set_last_cpu(state, smp_processor_id());
+	__this_cpu_write(fpsimd_owner, state);
+}
+
+void fpsimd_reset_lazy_restore(void)
+{
+	this_cpu_write(fpsimd_owner, NULL);
+}
+
 void fpsimd_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
 	fpsimd_save_state(&src->thread.fpsimd_state);
 	*dst = *src;
+	fpsimd_set_last_cpu(&dst->thread.fpsimd_state, -1);
 }
 
 void fpsimd_thread_switch(struct task_struct *next)
 {
 	/* check if not kernel threads */
 	if (current->mm)
-		fpsimd_save_state(&current->thread.fpsimd_state);
+		fpsimd_save_state_lazy(&current->thread.fpsimd_state);
 	if (next->mm)
-		fpsimd_load_state(&next->thread.fpsimd_state);
+		fpsimd_load_state_lazy(&next->thread.fpsimd_state);
 }
 
 void fpsimd_flush_thread(void)
@@ -107,6 +137,7 @@ void fpsimd_flush_thread(void)
 #if (AARCH64_FPCR_DEFAULT_VAL != 0)
 	state->fpcr = AARCH64_FPCR_DEFAULT_VAL;
 #endif
+	fpsimd_set_last_cpu(state, -1);
 	fpsimd_load_state(state);
 	preempt_enable();
 }
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 78db90d..aae15c4 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -183,6 +183,7 @@ asmlinkage void secondary_start_kernel(void)
 	 */
 	cpu_set_reserved_ttbr0();
 	flush_tlb_all();
+	fpsimd_reset_lazy_restore();
 
 	preempt_disable();
 	trace_hardirqs_off();
-- 
1.8.1.2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/