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    Subject[PATCH RESEND v9 29/36] x86/fred: FRED entry/exit and dispatch code
    Date
    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: Xin Li <xin3.li@intel.com>
    ---

    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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