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From:   Xin Li <xin3.li@intel.com>
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Subject: [PATCH v10 28/38] x86/fred: FRED entry/exit and dispatch code
Date:   Wed, 13 Sep 2023 21:47:55 -0700
Message-Id: <20230914044805.301390-29-xin3.li@intel.com>
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From: "H. Peter Anvin (Intel)" <hpa@zytor.com>

The code to actually handle kernel and event entry/exit using
FRED. It is split up into two files thus:

- entry_64_fred.S contains the actual entrypoints and exit code, and
  saves and restores registers.
- entry_fred.c contains the two-level event dispatch code for FRED.
  The first-level dispatch is on the event type, and the second-level
  is on the event vector.

Originally-by: Megha Dey <megha.dey@intel.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Co-developed-by: Xin Li <xin3.li@intel.com>
Tested-by: Shan Kang <shan.kang@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li <xin3.li@intel.com>
---

Changes since v9:
* Don't use jump tables, indirect jumps are expensive (Thomas Gleixner).
* Except NMI/#DB/#MCE, FRED really can share the exception handlers
  with IDT (Thomas Gleixner).
* Avoid the sysvec_* idt_entry muck, do it at a central place, reuse code
  instead of blindly copying it, which breaks the performance optimized
  sysvec entries like reschedule_ipi (Thomas Gleixner).
* Add asm_ prefix to FRED asm entry points (Thomas Gleixner).

Changes since v8:
* Don't do syscall early out in fred_entry_from_user() before there are
  proper performance numbers and justifications (Thomas Gleixner).
* Add the control exception handler to the FRED exception handler table
  (Thomas Gleixner).
* Add ENDBR to the FRED_ENTER asm macro.
* Reflect the FRED spec 5.0 change that ERETS and ERETU add 8 to %rsp
  before popping the return context from the stack.

Changes since v1:
* Initialize a FRED exception handler to fred_bad_event() instead of NULL
  if no FRED handler defined for an exception vector (Peter Zijlstra).
* Push calling irqentry_{enter,exit}() and instrumentation_{begin,end}()
  down into individual FRED exception handlers, instead of in the dispatch
  framework (Peter Zijlstra).
---
 arch/x86/entry/Makefile               |   5 +-
 arch/x86/entry/entry_64_fred.S        |  52 ++++++
 arch/x86/entry/entry_fred.c           | 230 ++++++++++++++++++++++++++
 arch/x86/include/asm/asm-prototypes.h |   1 +
 arch/x86/include/asm/fred.h           |   6 +
 5 files changed, 293 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/entry/entry_64_fred.S
 create mode 100644 arch/x86/entry/entry_fred.c

diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile
index ca2fe186994b..c93e7f5c2a06 100644
--- a/arch/x86/entry/Makefile
+++ b/arch/x86/entry/Makefile
@@ -18,6 +18,9 @@ obj-y				+= vdso/
 obj-y				+= vsyscall/
 
 obj-$(CONFIG_PREEMPTION)	+= thunk_$(BITS).o
+CFLAGS_entry_fred.o		+= -fno-stack-protector
+CFLAGS_REMOVE_entry_fred.o	+= -pg $(CC_FLAGS_FTRACE)
+obj-$(CONFIG_X86_FRED)		+= entry_64_fred.o entry_fred.o
+
 obj-$(CONFIG_IA32_EMULATION)	+= entry_64_compat.o syscall_32.o
 obj-$(CONFIG_X86_X32_ABI)	+= syscall_x32.o
-
diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S
new file mode 100644
index 000000000000..37a1dd5e8ace
--- /dev/null
+++ b/arch/x86/entry/entry_64_fred.S
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * The actual FRED entry points.
+ */
+
+#include <asm/fred.h>
+
+#include "calling.h"
+
+	.code64
+	.section .noinstr.text, "ax"
+
+.macro FRED_ENTER
+	UNWIND_HINT_END_OF_STACK
+	ENDBR
+	PUSH_AND_CLEAR_REGS
+	movq	%rsp, %rdi	/* %rdi -> pt_regs */
+.endm
+
+.macro FRED_EXIT
+	UNWIND_HINT_REGS
+	POP_REGS
+.endm
+
+/*
+ * The new RIP value that FRED event delivery establishes is
+ * IA32_FRED_CONFIG & ~FFFH for events that occur in ring 3.
+ * Thus the FRED ring 3 entry point must be 4K page aligned.
+ */
+	.align 4096
+
+SYM_CODE_START_NOALIGN(asm_fred_entrypoint_user)
+	FRED_ENTER
+	call	fred_entry_from_user
+	FRED_EXIT
+	ERETU
+SYM_CODE_END(asm_fred_entrypoint_user)
+
+.fill asm_fred_entrypoint_kernel - ., 1, 0xcc
+
+/*
+ * The new RIP value that FRED event delivery establishes is
+ * (IA32_FRED_CONFIG & ~FFFH) + 256 for events that occur in
+ * ring 0, i.e., asm_fred_entrypoint_user + 256.
+ */
+	.org asm_fred_entrypoint_user + 256
+SYM_CODE_START_NOALIGN(asm_fred_entrypoint_kernel)
+	FRED_ENTER
+	call	fred_entry_from_kernel
+	FRED_EXIT
+	ERETS
+SYM_CODE_END(asm_fred_entrypoint_kernel)
diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c
new file mode 100644
index 000000000000..dc645f5819a9
--- /dev/null
+++ b/arch/x86/entry/entry_fred.c
@@ -0,0 +1,230 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * The FRED specific kernel/user entry functions which are invoked from
+ * assembly code and dispatch to the associated handlers.
+ */
+#include <linux/kernel.h>
+#include <linux/kdebug.h>
+#include <linux/nospec.h>
+
+#include <asm/desc.h>
+#include <asm/fred.h>
+#include <asm/idtentry.h>
+#include <asm/syscall.h>
+#include <asm/trapnr.h>
+#include <asm/traps.h>
+
+/* FRED EVENT_TYPE_OTHER vector numbers */
+#define FRED_SYSCALL			1
+#define FRED_SYSENTER			2
+
+static noinstr void fred_bad_type(struct pt_regs *regs, unsigned long error_code)
+{
+	irqentry_state_t irq_state = irqentry_nmi_enter(regs);
+
+	instrumentation_begin();
+
+	/* Panic on events from a high stack level */
+	if (regs->sl > 0) {
+		pr_emerg("PANIC: invalid or fatal FRED event; event type %u "
+			 "vector %u error 0x%lx aux 0x%lx at %04x:%016lx\n",
+			 regs->fred_ss.type, regs->fred_ss.vector, regs->orig_ax,
+			 fred_event_data(regs), regs->cs, regs->ip);
+		die("invalid or fatal FRED event", regs, regs->orig_ax);
+		panic("invalid or fatal FRED event");
+	} else {
+		unsigned long flags = oops_begin();
+		int sig = SIGKILL;
+
+		pr_alert("BUG: invalid or fatal FRED event; event type %u "
+			 "vector %u error 0x%lx aux 0x%lx at %04x:%016lx\n",
+			 regs->fred_ss.type, regs->fred_ss.vector, regs->orig_ax,
+			 fred_event_data(regs), regs->cs, regs->ip);
+
+		if (__die("Invalid or fatal FRED event", regs, regs->orig_ax))
+			sig = 0;
+
+		oops_end(flags, regs, sig);
+	}
+
+	instrumentation_end();
+	irqentry_nmi_exit(regs, irq_state);
+}
+
+static noinstr void fred_intx(struct pt_regs *regs)
+{
+	switch (regs->fred_ss.vector) {
+	/* INT0 */
+	case X86_TRAP_OF:
+		exc_overflow(regs);
+		return;
+
+	/* INT3 */
+	case X86_TRAP_BP:
+		exc_int3(regs);
+		return;
+
+	/* INT80 */
+	case IA32_SYSCALL_VECTOR:
+		if (likely(IS_ENABLED(CONFIG_IA32_EMULATION))) {
+			/* Save the syscall number */
+			regs->orig_ax = regs->ax;
+			regs->ax = -ENOSYS;
+			do_int80_syscall_32(regs);
+			return;
+		}
+		fallthrough;
+
+	default:
+		exc_general_protection(regs, 0);
+		return;
+	}
+}
+
+static __always_inline void fred_other(struct pt_regs *regs)
+{
+	/* The compiler can fold these conditions into a single test */
+	if (likely(regs->fred_ss.vector == FRED_SYSCALL && regs->fred_ss.lm)) {
+		regs->orig_ax = regs->ax;
+		regs->ax = -ENOSYS;
+		do_syscall_64(regs, regs->orig_ax);
+		return;
+	} else if (likely(IS_ENABLED(CONFIG_IA32_EMULATION) &&
+			  regs->fred_ss.vector == FRED_SYSENTER &&
+			  !regs->fred_ss.lm)) {
+		regs->orig_ax = regs->ax;
+		regs->ax = -ENOSYS;
+		do_fast_syscall_32(regs);
+		return;
+	} else {
+		exc_invalid_op(regs);
+		return;
+	}
+}
+
+#define SYSVEC(_vector, _function) [_vector - FIRST_SYSTEM_VECTOR] = fred_sysvec_##_function
+
+static idtentry_t sysvec_table[NR_SYSTEM_VECTORS] __ro_after_init = {
+	SYSVEC(ERROR_APIC_VECTOR,		error_interrupt),
+	SYSVEC(SPURIOUS_APIC_VECTOR,		spurious_apic_interrupt),
+	SYSVEC(LOCAL_TIMER_VECTOR,		apic_timer_interrupt),
+	SYSVEC(X86_PLATFORM_IPI_VECTOR,		x86_platform_ipi),
+
+	SYSVEC(RESCHEDULE_VECTOR,		reschedule_ipi),
+	SYSVEC(CALL_FUNCTION_SINGLE_VECTOR,	call_function_single),
+	SYSVEC(CALL_FUNCTION_VECTOR,		call_function),
+	SYSVEC(REBOOT_VECTOR,			reboot),
+
+	SYSVEC(THRESHOLD_APIC_VECTOR,		threshold),
+	SYSVEC(DEFERRED_ERROR_VECTOR,		deferred_error),
+	SYSVEC(THERMAL_APIC_VECTOR,		thermal),
+
+	SYSVEC(IRQ_WORK_VECTOR,			irq_work),
+
+	SYSVEC(POSTED_INTR_VECTOR,		kvm_posted_intr_ipi),
+	SYSVEC(POSTED_INTR_WAKEUP_VECTOR,	kvm_posted_intr_wakeup_ipi),
+	SYSVEC(POSTED_INTR_NESTED_VECTOR,	kvm_posted_intr_nested_ipi),
+};
+
+static noinstr void fred_extint(struct pt_regs *regs)
+{
+	unsigned int vector = regs->fred_ss.vector;
+
+	if (WARN_ON_ONCE(vector < FIRST_EXTERNAL_VECTOR))
+		return;
+
+	if (likely(vector >= FIRST_SYSTEM_VECTOR)) {
+		irqentry_state_t state = irqentry_enter(regs);
+
+		instrumentation_begin();
+		sysvec_table[vector - FIRST_SYSTEM_VECTOR](regs);
+		instrumentation_end();
+		irqentry_exit(regs, state);
+	} else {
+		common_interrupt(regs, vector);
+	}
+}
+
+static noinstr void fred_exception(struct pt_regs *regs, unsigned long error_code)
+{
+	/* Optimize for #PF. That's the only exception which matters performance wise */
+	if (likely(regs->fred_ss.vector == X86_TRAP_PF)) {
+		exc_page_fault(regs, error_code);
+		return;
+	}
+
+	switch (regs->fred_ss.vector) {
+	case X86_TRAP_DE: return exc_divide_error(regs);
+	case X86_TRAP_DB: return fred_exc_debug(regs);
+	case X86_TRAP_BP: return exc_int3(regs);
+	case X86_TRAP_OF: return exc_overflow(regs);
+	case X86_TRAP_BR: return exc_bounds(regs);
+	case X86_TRAP_UD: return exc_invalid_op(regs);
+	case X86_TRAP_NM: return exc_device_not_available(regs);
+	case X86_TRAP_DF: return exc_double_fault(regs, error_code);
+	case X86_TRAP_TS: return exc_invalid_tss(regs, error_code);
+	case X86_TRAP_NP: return exc_segment_not_present(regs, error_code);
+	case X86_TRAP_SS: return exc_stack_segment(regs, error_code);
+	case X86_TRAP_GP: return exc_general_protection(regs, error_code);
+	case X86_TRAP_MF: return exc_coprocessor_error(regs);
+	case X86_TRAP_AC: return exc_alignment_check(regs, error_code);
+	case X86_TRAP_XF: return exc_simd_coprocessor_error(regs);
+
+#ifdef CONFIG_X86_MCE
+	case X86_TRAP_MC: return fred_exc_machine_check(regs);
+#endif
+#ifdef CONFIG_INTEL_TDX_GUEST
+	case X86_TRAP_VE: return exc_virtualization_exception(regs);
+#endif
+#ifdef CONFIG_X86_KERNEL_IBT
+	case X86_TRAP_CP: return exc_control_protection(regs, error_code);
+#endif
+	default: return fred_bad_type(regs, error_code);
+	}
+}
+
+__visible noinstr void fred_entry_from_user(struct pt_regs *regs)
+{
+	unsigned long error_code = regs->orig_ax;
+
+	/* Invalidate orig_ax so that syscall_get_nr() works correctly */
+	regs->orig_ax = -1;
+
+	switch (regs->fred_ss.type) {
+	case EVENT_TYPE_EXTINT:
+		return fred_extint(regs);
+	case EVENT_TYPE_NMI:
+		return fred_exc_nmi(regs);
+	case EVENT_TYPE_SWINT:
+		return fred_intx(regs);
+	case EVENT_TYPE_HWEXC:
+	case EVENT_TYPE_SWEXC:
+	case EVENT_TYPE_PRIV_SWEXC:
+		return fred_exception(regs, error_code);
+	case EVENT_TYPE_OTHER:
+		return fred_other(regs);
+	default:
+		return fred_bad_type(regs, error_code);
+	}
+}
+
+__visible noinstr void fred_entry_from_kernel(struct pt_regs *regs)
+{
+	unsigned long error_code = regs->orig_ax;
+
+	/* Invalidate orig_ax so that syscall_get_nr() works correctly */
+	regs->orig_ax = -1;
+
+	switch (regs->fred_ss.type) {
+	case EVENT_TYPE_EXTINT:
+		return fred_extint(regs);
+	case EVENT_TYPE_NMI:
+		return fred_exc_nmi(regs);
+	case EVENT_TYPE_HWEXC:
+	case EVENT_TYPE_SWEXC:
+	case EVENT_TYPE_PRIV_SWEXC:
+		return fred_exception(regs, error_code);
+	default:
+		return fred_bad_type(regs, error_code);
+	}
+}
diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index b1a98fa38828..076bf8dee702 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -12,6 +12,7 @@
 #include <asm/special_insns.h>
 #include <asm/preempt.h>
 #include <asm/asm.h>
+#include <asm/fred.h>
 #include <asm/gsseg.h>
 
 #ifndef CONFIG_X86_CMPXCHG64
diff --git a/arch/x86/include/asm/fred.h b/arch/x86/include/asm/fred.h
index f514fdb5a39f..16a64ffecbf8 100644
--- a/arch/x86/include/asm/fred.h
+++ b/arch/x86/include/asm/fred.h
@@ -60,6 +60,12 @@ static __always_inline unsigned long fred_event_data(struct pt_regs *regs)
 	return fred_info(regs)->edata;
 }
 
+void asm_fred_entrypoint_user(void);
+void asm_fred_entrypoint_kernel(void);
+
+__visible void fred_entry_from_user(struct pt_regs *regs);
+__visible void fred_entry_from_kernel(struct pt_regs *regs);
+
 #else /* CONFIG_X86_FRED */
 static __always_inline unsigned long fred_event_data(struct pt_regs *regs) { return 0; }
 #endif /* CONFIG_X86_FRED */
-- 
2.34.1