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Date: Wed, 12 Jun 2024 20:41:48 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>, linux-kernel@vger.kernel.org,
	Andy Lutomirski <luto@amacapital.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dave Hansen <dave@sr71.net>, Peter Zijlstra <peterz@infradead.org>,
	Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Uros Bizjak <ubizjak@gmail.com>
Subject: Re: [PATCH 3/9] x86/fpu: Make task_struct::thread constant size
Message-ID: <20240612184148.GB23973@redhat.com>
References: <20240608073134.264210-1-mingo@kernel.org>
 <20240608073134.264210-4-mingo@kernel.org>
 <20240610211350.GA1613053@thelio-3990X>
 <20240611124145.GA26798@redhat.com>
 <ZmlZiHVF8w09mExw@gmail.com>
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User-Agent: Mutt/1.5.24 (2015-08-30)

The patch below seems to fix the problem.

Again, the changes in fpu__init_system_early_generic() are not
strictly needed to fix it, but I believe make sense anyway.

Oleg.


diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 4e8d37b5a90b..848ea79886ba 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -71,16 +71,14 @@ static bool __init fpu__probe_without_cpuid(void)
 	return fsw == 0 && (fcw & 0x103f) == 0x003f;
 }
 
-static struct fpu x86_init_fpu __read_mostly;
+static struct fpu x86_init_fpu __attribute__ ((aligned (64))) __read_mostly;
 
 static void __init fpu__init_system_early_generic(void)
 {
-	int this_cpu = smp_processor_id();
-
 	fpstate_reset(&x86_init_fpu);
 	current->thread.fpu = &x86_init_fpu;
-	per_cpu(fpu_fpregs_owner_ctx, this_cpu) = &x86_init_fpu;
-	x86_init_fpu.last_cpu = this_cpu;
+	set_thread_flag(TIF_NEED_FPU_LOAD);
+	x86_init_fpu.last_cpu = -1;
 
 	if (!boot_cpu_has(X86_FEATURE_CPUID) &&
 	    !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 215a7380e41c..ec22b9bf27f5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1562,7 +1562,7 @@ struct task_struct {
 	 * they are included in the randomized portion of task_struct.
 	 */
 	randomized_struct_fields_end
-};
+} __attribute__ ((aligned (64)));
 
 #define TASK_REPORT_IDLE	(TASK_REPORT + 1)
 #define TASK_REPORT_MAX		(TASK_REPORT_IDLE << 1)