linux-kernel - [tip: x86/fred] x86/fred: Enable FRED right after init_mem

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Message-ID: <172357940456.2215.3119070109667388257.tip-bot2@tip-bot2>
Date: Tue, 13 Aug 2024 20:03:24 -0000
From: "tip-bot2 for Xin Li (Intel)" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Hou Wenlong <houwenlong.hwl@...group.com>,
 Thomas Gleixner <tglx@...utronix.de>, "Xin Li (Intel)" <xin@...or.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/fred] x86/fred: Enable FRED right after init_mem_mapping()

The following commit has been merged into the x86/fred branch of tip:

Commit-ID:     a97756cbec448032f84b5bbfe4e101478d1e01e0
Gitweb:        https://git.kernel.org/tip/a97756cbec448032f84b5bbfe4e101478d1e01e0
Author:        Xin Li (Intel) <xin@...or.com>
AuthorDate:    Tue, 09 Jul 2024 08:40:48 -07:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Tue, 13 Aug 2024 21:59:21 +02:00

x86/fred: Enable FRED right after init_mem_mapping()

On 64-bit init_mem_mapping() relies on the minimal page fault handler
provided by the early IDT mechanism. The real page fault handler is
installed right afterwards into the IDT.

This is problematic on CPUs which have X86_FEATURE_FRED set because the
real page fault handler retrieves the faulting address from the FRED
exception stack frame and not from CR2, but that does obviously not work
when FRED is not yet enabled in the CPU.

To prevent this enable FRED right after init_mem_mapping() without
interrupt stacks. Those are enabled later in trap_init() after the CPU
entry area is set up.

[ tglx: Encapsulate the FRED details ]

Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
Reported-by: Hou Wenlong <houwenlong.hwl@...group.com>
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Xin Li (Intel) <xin@...or.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/all/20240709154048.3543361-4-xin@zytor.com
---
 arch/x86/include/asm/processor.h |  3 ++-
 arch/x86/kernel/cpu/common.c     | 15 +++++++++++++--
 arch/x86/kernel/setup.c          |  7 ++++++-
 arch/x86/kernel/smpboot.c        |  2 +-
 arch/x86/kernel/traps.c          |  2 +-
 5 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index a75a07f..399f7d1 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -582,7 +582,8 @@ extern void switch_gdt_and_percpu_base(int);
 extern void load_direct_gdt(int);
 extern void load_fixmap_gdt(int);
 extern void cpu_init(void);
-extern void cpu_init_exception_handling(void);
+extern void cpu_init_exception_handling(bool boot_cpu);
+extern void cpu_init_replace_early_idt(void);
 extern void cr4_init(void);
 
 extern void set_task_blockstep(struct task_struct *task, bool on);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 6de12b3..a4735d9 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2176,7 +2176,7 @@ static inline void tss_setup_io_bitmap(struct tss_struct *tss)
  * Setup everything needed to handle exceptions from the IDT, including the IST
  * exceptions which use paranoid_entry().
  */
-void cpu_init_exception_handling(void)
+void cpu_init_exception_handling(bool boot_cpu)
 {
 	struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
 	int cpu = raw_smp_processor_id();
@@ -2196,13 +2196,24 @@ void cpu_init_exception_handling(void)
 	setup_ghcb();
 
 	if (cpu_feature_enabled(X86_FEATURE_FRED)) {
-		cpu_init_fred_exceptions();
+		/* The boot CPU has enabled FRED during early boot */
+		if (!boot_cpu)
+			cpu_init_fred_exceptions();
+
 		cpu_init_fred_rsps();
 	} else {
 		load_current_idt();
 	}
 }
 
+void __init cpu_init_replace_early_idt(void)
+{
+	if (cpu_feature_enabled(X86_FEATURE_FRED))
+		cpu_init_fred_exceptions();
+	else
+		idt_setup_early_pf();
+}
+
 /*
  * cpu_init() initializes state that is per-CPU. Some data is already
  * initialized (naturally) in the bootstrap process, such as the GDT.  We
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 6129dc2..f1fea50 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1039,7 +1039,12 @@ void __init setup_arch(char **cmdline_p)
 
 	init_mem_mapping();
 
-	idt_setup_early_pf();
+	/*
+	 * init_mem_mapping() relies on the early IDT page fault handling.
+	 * Now either enable FRED or install the real page fault handler
+	 * for 64-bit in the IDT.
+	 */
+	cpu_init_replace_early_idt();
 
 	/*
 	 * Update mmu_cr4_features (and, indirectly, trampoline_cr4_features)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 0c35207..dc4fff8 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -246,7 +246,7 @@ static void notrace start_secondary(void *unused)
 		__flush_tlb_all();
 	}
 
-	cpu_init_exception_handling();
+	cpu_init_exception_handling(false);
 
 	/*
 	 * Load the microcode before reaching the AP alive synchronization
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 6afb41e..197d588 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1411,7 +1411,7 @@ void __init trap_init(void)
 	sev_es_init_vc_handling();
 
 	/* Initialize TSS before setting up traps so ISTs work */
-	cpu_init_exception_handling();
+	cpu_init_exception_handling(true);
 
 	/* Setup traps as cpu_init() might #GP */
 	if (!cpu_feature_enabled(X86_FEATURE_FRED))