[PATCH RESEND v9 29/36] x86/fred: FRED entry/exit and dispatch code

From: Xin Li
Date: Tue Aug 01 2023 - 05:09:22 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: Xin Li <xin3.li@xxxxxxxxx>
---

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 | 53 +++++++
arch/x86/entry/entry_fred.c | 220 ++++++++++++++++++++++++++
arch/x86/include/asm/asm-prototypes.h | 1 +
arch/x86/include/asm/fred.h | 4 +
arch/x86/include/asm/idtentry.h | 4 +
6 files changed, 286 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..4ae12d557db3
--- /dev/null
+++ b/arch/x86/entry/entry_64_fred.S
@@ -0,0 +1,53 @@
+/* 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(fred_entrypoint_user)
+ FRED_ENTER
+ call fred_entry_from_user
+SYM_INNER_LABEL(fred_exit_user, SYM_L_GLOBAL)
+ FRED_EXIT
+ ERETU
+SYM_CODE_END(fred_entrypoint_user)
+
+.fill 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., fred_entrypoint_user + 256.
+ */
+ .org fred_entrypoint_user+256
+SYM_CODE_START_NOALIGN(fred_entrypoint_kernel)
+ FRED_ENTER
+ call fred_entry_from_kernel
+ FRED_EXIT
+ ERETS
+SYM_CODE_END(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..1688e7e09370
--- /dev/null
+++ b/arch/x86/entry/entry_fred.c
@@ -0,0 +1,220 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * This contains the dispatch functions called from the entry point
+ * assembly.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kdebug.h>
+#include <linux/nospec.h>
+
+#include <asm/fred.h>
+#include <asm/idtentry.h>
+#include <asm/syscall.h>
+#include <asm/trapnr.h>
+#include <asm/traps.h>
+#include <asm/kdebug.h>
+
+static DEFINE_FRED_HANDLER(fred_bad_event)
+{
+ 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->type, regs->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->type, regs->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 DEFINE_FRED_HANDLER(fred_exception)
+{
+ /*
+ * Exceptions that cannot happen on FRED h/w are set to fred_bad_event().
+ */
+ static const fred_handler exception_handlers[NUM_EXCEPTION_VECTORS] = {
+ [0 ... NUM_EXCEPTION_VECTORS-1] = fred_bad_event,
+
+ [X86_TRAP_DE] = exc_divide_error,
+ [X86_TRAP_DB] = fred_exc_debug,
+ [X86_TRAP_BP] = exc_int3,
+ [X86_TRAP_OF] = exc_overflow,
+ [X86_TRAP_BR] = exc_bounds,
+ [X86_TRAP_UD] = exc_invalid_op,
+ [X86_TRAP_NM] = exc_device_not_available,
+ [X86_TRAP_DF] = fred_exc_double_fault,
+ [X86_TRAP_TS] = fred_exc_invalid_tss,
+ [X86_TRAP_NP] = fred_exc_segment_not_present,
+ [X86_TRAP_SS] = fred_exc_stack_segment,
+ [X86_TRAP_GP] = fred_exc_general_protection,
+ [X86_TRAP_PF] = fred_exc_page_fault,
+ [X86_TRAP_MF] = exc_coprocessor_error,
+ [X86_TRAP_AC] = fred_exc_alignment_check,
+ [X86_TRAP_MC] = fred_exc_machine_check,
+ [X86_TRAP_XF] = exc_simd_coprocessor_error,
+ [X86_TRAP_CP] = fred_exc_control_protection,
+ };
+
+ exception_handlers[regs->vector](regs);
+}
+
+static __always_inline void fred_emulate_trap(struct pt_regs *regs)
+{
+ regs->orig_ax = 0;
+ fred_exception(regs);
+}
+
+static __always_inline void fred_emulate_fault(struct pt_regs *regs)
+{
+ regs->ip -= regs->instr_len;
+ fred_emulate_trap(regs);
+}
+
+static DEFINE_FRED_HANDLER(fred_sw_interrupt_user)
+{
+ /*
+ * In compat mode INT $0x80 (32bit system call) is
+ * performance-critical. Handle it first.
+ */
+ if (IS_ENABLED(CONFIG_IA32_EMULATION) &&
+ likely(regs->vector == IA32_SYSCALL_VECTOR)) {
+ regs->orig_ax = regs->ax;
+ regs->ax = -ENOSYS;
+ return do_int80_syscall_32(regs);
+ }
+
+ /*
+ * Some software exceptions can also be triggered as
+ * int instructions, for historical reasons.
+ */
+ switch (regs->vector) {
+ case X86_TRAP_BP:
+ case X86_TRAP_OF:
+ fred_emulate_trap(regs);
+ break;
+ default:
+ regs->vector = X86_TRAP_GP;
+ fred_emulate_fault(regs);
+ break;
+ }
+}
+
+static DEFINE_FRED_HANDLER(fred_other_default)
+{
+ regs->vector = X86_TRAP_UD;
+ fred_emulate_fault(regs);
+}
+
+static DEFINE_FRED_HANDLER(fred_syscall)
+{
+ regs->orig_ax = regs->ax;
+ regs->ax = -ENOSYS;
+ do_syscall_64(regs, regs->orig_ax);
+}
+
+#if IS_ENABLED(CONFIG_IA32_EMULATION)
+/*
+ * Emulate SYSENTER if applicable. This is not the preferred system
+ * call in 32-bit mode under FRED, rather int $0x80 is preferred and
+ * exported in the vdso.
+ */
+static DEFINE_FRED_HANDLER(fred_sysenter)
+{
+ regs->orig_ax = regs->ax;
+ regs->ax = -ENOSYS;
+ do_fast_syscall_32(regs);
+}
+#else
+#define fred_sysenter fred_other_default
+#endif
+
+static DEFINE_FRED_HANDLER(fred_other)
+{
+ static const fred_handler user_other_handlers[FRED_NUM_OTHER_VECTORS] =
+ {
+ /*
+ * Vector 0 of the other event type is not used
+ * per FRED spec 5.0.
+ */
+ [0] = fred_other_default,
+ [FRED_SYSCALL] = fred_syscall,
+ [FRED_SYSENTER] = fred_sysenter
+ };
+
+ user_other_handlers[regs->vector](regs);
+}
+
+static DEFINE_FRED_HANDLER(fred_hw_interrupt)
+{
+ irqentry_state_t state = irqentry_enter(regs);
+
+ instrumentation_begin();
+ external_interrupt(regs);
+ instrumentation_end();
+ irqentry_exit(regs, state);
+}
+
+__visible noinstr void fred_entry_from_user(struct pt_regs *regs)
+{
+ static const fred_handler user_handlers[FRED_EVENT_TYPE_COUNT] =
+ {
+ [EVENT_TYPE_HWINT] = fred_hw_interrupt,
+ [EVENT_TYPE_RESERVED] = fred_bad_event,
+ [EVENT_TYPE_NMI] = fred_exc_nmi,
+ [EVENT_TYPE_SWINT] = fred_sw_interrupt_user,
+ [EVENT_TYPE_HWFAULT] = fred_exception,
+ [EVENT_TYPE_SWFAULT] = fred_exception,
+ [EVENT_TYPE_PRIVSW] = fred_exception,
+ [EVENT_TYPE_OTHER] = fred_other
+ };
+
+ /*
+ * FRED employs a two-level event dispatch mechanism, with the
+ * first-level on the type of an event and the second-level on
+ * its vector. Here is the first-level dispatch for ring 3 events.
+ */
+ user_handlers[regs->type](regs);
+}
+
+__visible noinstr void fred_entry_from_kernel(struct pt_regs *regs)
+{
+ static const fred_handler kernel_handlers[FRED_EVENT_TYPE_COUNT] =
+ {
+ [EVENT_TYPE_HWINT] = fred_hw_interrupt,
+ [EVENT_TYPE_RESERVED] = fred_bad_event,
+ [EVENT_TYPE_NMI] = fred_exc_nmi,
+ [EVENT_TYPE_SWINT] = fred_bad_event,
+ [EVENT_TYPE_HWFAULT] = fred_exception,
+ [EVENT_TYPE_SWFAULT] = fred_exception,
+ [EVENT_TYPE_PRIVSW] = fred_exception,
+ [EVENT_TYPE_OTHER] = fred_bad_event
+ };
+
+ /*
+ * FRED employs a two-level event dispatch mechanism, with the
+ * first-level on the type of an event and the second-level on
+ * its vector. Here is the first-level dispatch for ring 0 events.
+ */
+ kernel_handlers[regs->type](regs);
+}
diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index b1a98fa38828..36505b991f88 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -13,6 +13,7 @@
#include <asm/preempt.h>
#include <asm/asm.h>
#include <asm/gsseg.h>
+#include <asm/fred.h>

#ifndef CONFIG_X86_CMPXCHG64
extern void cmpxchg8b_emu(void);
diff --git a/arch/x86/include/asm/fred.h b/arch/x86/include/asm/fred.h
index bd701ac87528..3c91f0eae62e 100644
--- a/arch/x86/include/asm/fred.h
+++ b/arch/x86/include/asm/fred.h
@@ -118,6 +118,10 @@ DECLARE_FRED_HANDLER(fred_exc_page_fault);
DECLARE_FRED_HANDLER(fred_exc_machine_check);
DECLARE_FRED_HANDLER(fred_exc_double_fault);

+/* The actual assembly entry point for ring 3 and 0 */
+extern asmlinkage __visible void fred_entrypoint_user(void);
+extern asmlinkage __visible void fred_entrypoint_kernel(void);
+
#endif /* __ASSEMBLY__ */

#endif /* CONFIG_X86_FRED */
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 3b743c3fbe91..0df3a3cc7e0f 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -661,6 +661,8 @@ DECLARE_IDTENTRY_RAW(X86_TRAP_MC, exc_machine_check);
#ifdef CONFIG_XEN_PV
DECLARE_IDTENTRY_RAW(X86_TRAP_MC, xenpv_exc_machine_check);
#endif
+#else
+#define fred_exc_machine_check fred_bad_event
#endif

/* NMI */
@@ -699,6 +701,8 @@ DECLARE_IDTENTRY_RAW_ERRORCODE(X86_TRAP_DF, xenpv_exc_double_fault);
/* #CP */
#ifdef CONFIG_X86_KERNEL_IBT
DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_CP, exc_control_protection);
+#else
+#define fred_exc_control_protection fred_bad_event
#endif

/* #VC */
--
2.34.1

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