[PATCH v12 28/37] x86/fred: FRED entry/exit and dispatch code

From: Xin Li
Date: Tue Oct 03 2023 - 02:56:46 EST

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

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@xxxxxxxxx>
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: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---

Changes since v10:
* Replace "IS_ENABLED(CONFIG_IA32_EMULATION)" with the new ia32_enabled()
API (Nikolay Borisov).

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..215883e90f94
--- /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->fred_cs.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 (ia32_enabled()) {
+ /* 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 (ia32_enabled() &&
+ likely(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

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