[PATCH v9 35/36] x86/fred: FRED initialization code
From: Xin Li
Date: Mon Jul 31 2023 - 03:13:56 EST
From: "H. Peter Anvin (Intel)" <hpa@xxxxxxxxx>
The code to initialize FRED when it's available and _not_ disabled.
cpu_init_fred_exceptions() is the core function to initialize FRED,
which
1. Sets up FRED entrypoints for events happening in ring 0 and 3.
2. Sets up a default stack for event handling.
3. Sets up dedicated event stacks for DB/NMI/MC/DF, equivalent to
the IDT IST stacks.
4. Forces 32-bit system calls to use "int $0x80" only.
5. Enables FRED and invalidtes IDT.
When the FRED is used, cpu_init_exception_handling() initializes FRED
through calling cpu_init_fred_exceptions(), otherwise it sets up TSS
IST and loads IDT.
As FRED uses the ring 3 FRED entrypoint for SYSCALL and SYSENTER,
it skips setting up SYSCALL/SYSENTER related MSRs, e.g., MSR_LSTAR.
Signed-off-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Co-developed-by: Xin Li <xin3.li@xxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---
Changes since v8:
* Move this patch after all required changes are in place (Thomas
Gleixner).
Changes since v5:
* Add a comment for FRED stack level settings (Lai Jiangshan).
* Define #DB/NMI/#MC/#DF stack levels using macros.
---
arch/x86/include/asm/fred.h | 28 ++++++++++++++++
arch/x86/include/asm/traps.h | 4 ++-
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/cpu/common.c | 28 +++++++++++++---
arch/x86/kernel/fred.c | 64 ++++++++++++++++++++++++++++++++++++
arch/x86/kernel/irqinit.c | 7 +++-
arch/x86/kernel/traps.c | 11 ++++++-
7 files changed, 135 insertions(+), 8 deletions(-)
create mode 100644 arch/x86/kernel/fred.c
diff --git a/arch/x86/include/asm/fred.h b/arch/x86/include/asm/fred.h
index 3c91f0eae62e..6031138b778c 100644
--- a/arch/x86/include/asm/fred.h
+++ b/arch/x86/include/asm/fred.h
@@ -68,6 +68,19 @@
#define FRED_SSX_64_BIT_MODE_BIT 57
#define FRED_SSX_64_BIT_MODE _BITUL(FRED_SSX_64_BIT_MODE_BIT)
+/* #DB in the kernel would imply the use of a kernel debugger. */
+#define FRED_DB_STACK_LEVEL 1
+#define FRED_NMI_STACK_LEVEL 2
+#define FRED_MC_STACK_LEVEL 2
+/*
+ * #DF is the highest level because a #DF means "something went wrong
+ * *while delivering an exception*." The number of cases for which that
+ * can happen with FRED is drastically reduced and basically amounts to
+ * "the stack you pointed me to is broken." Thus, always change stacks
+ * on #DF, which means it should be at the highest level.
+ */
+#define FRED_DF_STACK_LEVEL 3
+
/*
* FRED event delivery establishes a full supervisor context by
* saving the essential information about an event to a FRED
@@ -122,8 +135,23 @@ DECLARE_FRED_HANDLER(fred_exc_double_fault);
extern asmlinkage __visible void fred_entrypoint_user(void);
extern asmlinkage __visible void fred_entrypoint_kernel(void);
+void cpu_init_fred_exceptions(void);
+void fred_setup_apic(void);
+
#endif /* __ASSEMBLY__ */
+#else
+#ifndef __ASSEMBLY__
+static inline void cpu_init_fred_exceptions(void)
+{
+ BUG();
+}
+
+static inline void fred_setup_apic(void)
+{
+ BUG();
+}
+#endif
#endif /* CONFIG_X86_FRED */
#endif /* ASM_X86_FRED_H */
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 48daa78ee88c..da7e8ab1d66d 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -49,6 +49,7 @@ void __noreturn handle_stack_overflow(struct pt_regs *regs,
#ifdef CONFIG_X86_64
inline void set_sysvec_handler(unsigned int i, system_interrupt_handler func);
+bool is_sysvec_used(unsigned int i);
static inline void sysvec_setup_fred(unsigned int vector, system_interrupt_handler func)
{
@@ -63,7 +64,8 @@ static inline void sysvec_setup_fred(unsigned int vector, system_interrupt_handl
#define sysvec_install(vector, func) { \
sysvec_setup_fred(vector, func); \
- alloc_intr_gate(vector, asm_##func); \
+ if (!cpu_feature_enabled(X86_FEATURE_FRED)) \
+ alloc_intr_gate(vector, asm_##func); \
}
int external_interrupt(struct pt_regs *regs);
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 4070a01c11b7..46d8daa11c17 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -48,6 +48,7 @@ obj-y += platform-quirks.o
obj-y += process_$(BITS).o signal.o signal_$(BITS).o
obj-y += traps.o idt.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
obj-y += time.o ioport.o dumpstack.o nmi.o
+obj-$(CONFIG_X86_FRED) += fred.o
obj-$(CONFIG_MODIFY_LDT_SYSCALL) += ldt.o
obj-y += setup.o x86_init.o i8259.o irqinit.o
obj-$(CONFIG_JUMP_LABEL) += jump_label.o
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index bb03dacc5fb8..b34a8a138755 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -62,6 +62,7 @@
#include <asm/microcode_intel.h>
#include <asm/intel-family.h>
#include <asm/cpu_device_id.h>
+#include <asm/fred.h>
#include <asm/uv/uv.h>
#include <asm/set_memory.h>
#include <asm/traps.h>
@@ -2062,13 +2063,24 @@ static inline void idt_syscall_init(void)
X86_EFLAGS_AC|X86_EFLAGS_ID);
}
+static inline void fred_syscall_init(void)
+{
+ /* Both sysexit and sysret cause #UD when FRED is enabled */
+ wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);
+ wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
+ wrmsrl_safe(MSR_IA32_SYSENTER_EIP, 0ULL);
+}
+
/* May not be marked __init: used by software suspend */
void syscall_init(void)
{
/* The default user and kernel segments */
wrmsr(MSR_STAR, 0, (__USER32_CS << 16) | __KERNEL_CS);
- idt_syscall_init();
+ if (cpu_feature_enabled(X86_FEATURE_FRED))
+ fred_syscall_init();
+ else
+ idt_syscall_init();
}
#else /* CONFIG_X86_64 */
@@ -2184,8 +2196,6 @@ void cpu_init_exception_handling(void)
/* paranoid_entry() gets the CPU number from the GDT */
setup_getcpu(cpu);
- /* IST vectors need TSS to be set up. */
- tss_setup_ist(tss);
tss_setup_io_bitmap(tss);
set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
@@ -2194,8 +2204,16 @@ void cpu_init_exception_handling(void)
/* GHCB needs to be setup to handle #VC. */
setup_ghcb();
- /* Finally load the IDT */
- load_current_idt();
+ if (cpu_feature_enabled(X86_FEATURE_FRED)) {
+ /* Set up FRED exception handling */
+ cpu_init_fred_exceptions();
+ } else {
+ /* IST vectors need TSS to be set up. */
+ tss_setup_ist(tss);
+
+ /* Finally load the IDT */
+ load_current_idt();
+ }
}
/*
diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c
new file mode 100644
index 000000000000..7fdf79c964a8
--- /dev/null
+++ b/arch/x86/kernel/fred.c
@@ -0,0 +1,64 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/kernel.h>
+
+#include <asm/desc.h>
+#include <asm/fred.h>
+#include <asm/tlbflush.h>
+#include <asm/traps.h>
+
+void cpu_init_fred_exceptions(void)
+{
+ wrmsrl(MSR_IA32_FRED_CONFIG,
+ /* Reserve for CALL emulation */
+ FRED_CONFIG_REDZONE |
+ FRED_CONFIG_INT_STKLVL(0) |
+ FRED_CONFIG_ENTRYPOINT(fred_entrypoint_user));
+
+ /*
+ * The purpose of separate stacks for NMI, #DB and #MC *in the kernel*
+ * (remember that user space faults are always taken on stack level 0)
+ * is to avoid overflowing the kernel stack.
+ */
+ wrmsrl(MSR_IA32_FRED_STKLVLS,
+ FRED_STKLVL(X86_TRAP_DB, FRED_DB_STACK_LEVEL) |
+ FRED_STKLVL(X86_TRAP_NMI, FRED_NMI_STACK_LEVEL) |
+ FRED_STKLVL(X86_TRAP_MC, FRED_MC_STACK_LEVEL) |
+ FRED_STKLVL(X86_TRAP_DF, FRED_DF_STACK_LEVEL));
+
+ /* The FRED equivalents to IST stacks... */
+ wrmsrl(MSR_IA32_FRED_RSP1, __this_cpu_ist_top_va(DB));
+ wrmsrl(MSR_IA32_FRED_RSP2, __this_cpu_ist_top_va(NMI));
+ wrmsrl(MSR_IA32_FRED_RSP3, __this_cpu_ist_top_va(DF));
+
+ /* Not used with FRED */
+ wrmsrl(MSR_LSTAR, 0ULL);
+ wrmsrl(MSR_CSTAR, 0ULL);
+ wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);
+ wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
+ wrmsrl_safe(MSR_IA32_SYSENTER_EIP, 0ULL);
+
+ /* Enable FRED */
+ cr4_set_bits(X86_CR4_FRED);
+ /* Any further IDT use is a bug */
+ idt_invalidate();
+
+ /* Use int $0x80 for 32-bit system calls in FRED mode */
+ setup_clear_cpu_cap(X86_FEATURE_SYSENTER32);
+ setup_clear_cpu_cap(X86_FEATURE_SYSCALL32);
+}
+
+/*
+ * Initialize system vectors from a FRED perspective, so
+ * lapic_assign_system_vectors() can do its job.
+ */
+void __init fred_setup_apic(void)
+{
+ int i;
+
+ for (i = 0; i < FIRST_EXTERNAL_VECTOR; i++)
+ set_bit(i, system_vectors);
+
+ for (i = 0; i < NR_SYSTEM_VECTORS; i++)
+ if (is_sysvec_used(i))
+ set_bit(i + FIRST_SYSTEM_VECTOR, system_vectors);
+}
diff --git a/arch/x86/kernel/irqinit.c b/arch/x86/kernel/irqinit.c
index c683666876f1..2a510f72dd11 100644
--- a/arch/x86/kernel/irqinit.c
+++ b/arch/x86/kernel/irqinit.c
@@ -28,6 +28,7 @@
#include <asm/setup.h>
#include <asm/i8259.h>
#include <asm/traps.h>
+#include <asm/fred.h>
#include <asm/prom.h>
/*
@@ -96,7 +97,11 @@ void __init native_init_IRQ(void)
/* Execute any quirks before the call gates are initialised: */
x86_init.irqs.pre_vector_init();
- idt_setup_apic_and_irq_gates();
+ if (cpu_feature_enabled(X86_FEATURE_FRED))
+ fred_setup_apic();
+ else
+ idt_setup_apic_and_irq_gates();
+
lapic_assign_system_vectors();
if (!acpi_ioapic && !of_ioapic && nr_legacy_irqs()) {
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 6143ad56008e..21eeba7b188f 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1542,6 +1542,12 @@ void set_sysvec_handler(unsigned int i, system_interrupt_handler func)
system_interrupt_handlers[i] = func;
}
+bool is_sysvec_used(unsigned int i)
+{
+ BUG_ON(i >= NR_SYSTEM_VECTORS);
+ return system_interrupt_handlers[i] != dispatch_table_spurious_interrupt;
+}
+
int external_interrupt(struct pt_regs *regs)
{
unsigned int vector = regs->vector;
@@ -1577,7 +1583,10 @@ void __init trap_init(void)
/* Initialize TSS before setting up traps so ISTs work */
cpu_init_exception_handling();
+
/* Setup traps as cpu_init() might #GP */
- idt_setup_traps();
+ if (!cpu_feature_enabled(X86_FEATURE_FRED))
+ idt_setup_traps();
+
cpu_init();
}
--
2.34.1