[PATCH v13 34/35] x86/fred: Add FRED initialization functions

Xin Li
2023-12-05T11:23:31Z

From: "H. Peter Anvin (Intel)" <hpa@zytor.com>

Add cpu_init_fred_exceptions() to:
- Set FRED entrypoints for events happening in ring 0 and 3.
- Specify the stack level for IRQs occurred ring 0.
- Specify dedicated event stacks for #DB/NMI/#MCE/#DF.
- Enable FRED and invalidtes IDT.
- Force 32-bit system calls to use "int $0x80" only.

Add fred_complete_exception_setup() to:
- Initialize system_vectors as done for IDT systems.
- Set unused sysvec_table entries to fred_handle_spurious_interrupt().

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Tested-by: Shan Kang <shan.kang@intel.com>
Co-developed-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---

Changes since v9:
* Set unused sysvec table entries to fred_handle_spurious_interrupt()
in fred_complete_exception_setup() (Thomas Gleixner).

Changes since v5:
* Add a comment for FRED stack level settings (Lai Jiangshan).
* Define NMI/#DB/#MCE/#DF stack levels using macros.
---
arch/x86/entry/entry_fred.c | 21 +++++++++++++
arch/x86/include/asm/fred.h | 5 ++++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/fred.c | 59 +++++++++++++++++++++++++++++++++++++
4 files changed, 86 insertions(+)
create mode 100644 arch/x86/kernel/fred.c

diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c
index 3e33a4ab4624..abe66d65fa2d 100644
--- a/arch/x86/entry/entry_fred.c
+++ b/arch/x86/entry/entry_fred.c
@@ -140,6 +140,27 @@ void __init fred_install_sysvec(unsigned int sysvec, idtentry_t handler)
sysvec_table[sysvec - FIRST_SYSTEM_VECTOR] = handler;
}

+static noinstr void fred_handle_spurious_interrupt(struct pt_regs *regs)
+{
+ spurious_interrupt(regs, regs->fred_ss.vector);
+}
+
+void __init fred_complete_exception_setup(void)
+{
+ unsigned int vector;
+
+ for (vector = 0; vector < FIRST_EXTERNAL_VECTOR; vector++)
+ set_bit(vector, system_vectors);
+
+ for (vector = 0; vector < NR_SYSTEM_VECTORS; vector++) {
+ if (sysvec_table[vector])
+ set_bit(vector + FIRST_SYSTEM_VECTOR, system_vectors);
+ else
+ sysvec_table[vector] = fred_handle_spurious_interrupt;
+ }
+ fred_setup_done = true;
+}
+
static noinstr void fred_extint(struct pt_regs *regs)
{
unsigned int vector = regs->fred_ss.vector;
diff --git a/arch/x86/include/asm/fred.h b/arch/x86/include/asm/fred.h
index 2fa9f34e5c95..e86c7ba32435 100644
--- a/arch/x86/include/asm/fred.h
+++ b/arch/x86/include/asm/fred.h
@@ -83,8 +83,13 @@ static __always_inline void fred_entry_from_kvm(unsigned int type, unsigned int
asm_fred_entry_from_kvm(ss);
}

+void cpu_init_fred_exceptions(void);
+void fred_complete_exception_setup(void);
+
#else /* CONFIG_X86_FRED */
static __always_inline unsigned long fred_event_data(struct pt_regs *regs) { return 0; }
+static inline void cpu_init_fred_exceptions(void) { }
+static inline void fred_complete_exception_setup(void) { }
static __always_inline void fred_entry_from_kvm(unsigned int type, unsigned int vector) { }
#endif /* CONFIG_X86_FRED */
#endif /* !__ASSEMBLY__ */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 0000325ab98f..0dcbfc1a4c41 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-$(CONFIG_X86_KERNEL_IBT) += ibt_selftest.o
obj-y += setup.o x86_init.o i8259.o irqinit.o
diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c
new file mode 100644
index 000000000000..4bcd8791ad96
--- /dev/null
+++ b/arch/x86/kernel/fred.c
@@ -0,0 +1,59 @@
+/* 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>
+
+/* #DB in the kernel would imply the use of a kernel debugger. */
+#define FRED_DB_STACK_LEVEL 1UL
+#define FRED_NMI_STACK_LEVEL 2UL
+#define FRED_MC_STACK_LEVEL 2UL
+/*
+ * #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 3UL
+
+#define FRED_STKLVL(vector, lvl) ((lvl) << (2 * (vector)))
+
+void cpu_init_fred_exceptions(void)
+{
+ /* When FRED is enabled by default, remove this log message */
+ pr_info("Initialize FRED on CPU%d\n", smp_processor_id());
+
+ wrmsrl(MSR_IA32_FRED_CONFIG,
+ /* Reserve for CALL emulation */
+ FRED_CONFIG_REDZONE |
+ FRED_CONFIG_INT_STKLVL(0) |
+ FRED_CONFIG_ENTRYPOINT(asm_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));
+
+ /* 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);
+}
--
2.43.0