[PATCH] x86/cpu: Init exception handling from cpu_init()

[PATCH] x86/cpu: Init exception handling from cpu_init()

[Borislav Petkov]

From: Borislav Petkov <bp@suse.de>

SEV-ES guests require properly setup task register with which the TSS
descriptor in the GDT can be located so that the IST-type #VC exception
handler which they need to function properly, can be executed.

This setup needs to happen before attempting to load microcode in
ucode_cpu_init() which can cause such #VC exceptions.

Simplify the machinery by running that exception setup from cpu_init()
directly.

There should be no functional changes resulting from this patch.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/include/asm/processor.h |  1 -
 arch/x86/kernel/cpu/common.c     | 14 +++-----------
 arch/x86/kernel/smpboot.c        |  1 -
 3 files changed, 3 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 154321d29050..50059c988167 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -663,7 +663,6 @@ extern void load_direct_gdt(int);
 extern void load_fixmap_gdt(int);
 extern void load_percpu_segment(int);
 extern void cpu_init(void);
-extern void cpu_init_exception_handling(void);
 extern void cr4_init(void);
 
 static inline unsigned long get_debugctlmsr(void)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 6bdb69a9a7dc..1aa20b5e4e66 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1917,7 +1917,7 @@ 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)
+static void init_exception_handling(void)
 {
 	struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
 	int cpu = raw_smp_processor_id();
@@ -1944,10 +1944,11 @@ void cpu_init_exception_handling(void)
  */
 void cpu_init(void)
 {
-	struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
 	struct task_struct *cur = current;
 	int cpu = raw_smp_processor_id();
 
+	init_exception_handling();
+
 	wait_for_master_cpu(cpu);
 
 	ucode_cpu_init(cpu);
@@ -1957,8 +1958,6 @@ void cpu_init(void)
 	    early_cpu_to_node(cpu) != NUMA_NO_NODE)
 		set_numa_node(early_cpu_to_node(cpu));
 #endif
-	setup_getcpu(cpu);
-
 	pr_debug("Initializing CPU#%d\n", cpu);
 
 	if (IS_ENABLED(CONFIG_X86_64) || cpu_feature_enabled(X86_FEATURE_VME) ||
@@ -1970,7 +1969,6 @@ void cpu_init(void)
 	 * and set up the GDT descriptor:
 	 */
 	switch_to_new_gdt(cpu);
-	load_current_idt();
 
 	if (IS_ENABLED(CONFIG_X86_64)) {
 		loadsegment(fs, 0);
@@ -1990,12 +1988,6 @@ void cpu_init(void)
 	initialize_tlbstate_and_flush();
 	enter_lazy_tlb(&init_mm, cur);
 
-	/* Initialize the TSS. */
-	tss_setup_ist(tss);
-	tss_setup_io_bitmap(tss);
-	set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
-
-	load_TR_desc();
 	/*
 	 * sp0 points to the entry trampoline stack regardless of what task
 	 * is running.
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 7ffb0cf3f997..5e5899d046e4 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -232,7 +232,6 @@ static void notrace start_secondary(void *unused)
 	load_cr3(swapper_pg_dir);
 	__flush_tlb_all();
 #endif
-	cpu_init_exception_handling();
 	cpu_init();
 	rcu_cpu_starting(raw_smp_processor_id());
 	x86_cpuinit.early_percpu_clock_init();
-- 
2.29.2

Re: [PATCH] x86/cpu: Init exception handling from cpu_init()

[Joerg Roedel]

On Tue, May 04, 2021 at 07:17:45PM +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@suse.de>
> 
> SEV-ES guests require properly setup task register with which the TSS
> descriptor in the GDT can be located so that the IST-type #VC exception
> handler which they need to function properly, can be executed.
> 
> This setup needs to happen before attempting to load microcode in
> ucode_cpu_init() which can cause such #VC exceptions.
> 
> Simplify the machinery by running that exception setup from cpu_init()
> directly.
> 
> There should be no functional changes resulting from this patch.
> 
> Signed-off-by: Borislav Petkov <bp@suse.de>
> ---
>  arch/x86/include/asm/processor.h |  1 -
>  arch/x86/kernel/cpu/common.c     | 14 +++-----------
>  arch/x86/kernel/smpboot.c        |  1 -
>  3 files changed, 3 insertions(+), 13 deletions(-)

Acked-by: Joerg Roedel <jroedel@suse.de>