[PATCH v9 35/36] x86/fred: FRED initialization code

[Xin Li <xin3.li@xxxxxxxxx>]

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