[PATCH v7 00/33] x86: enable FRED for x86-64

Xin Li
2023-04-04T10:53:48Z

This patch set enables FRED for x86-64.

The Intel flexible return and event delivery (FRED) architecture defines simple
new transitions that change privilege level (ring transitions). The FRED
architecture was designed with the following goals:
1) Improve overall performance and response time by replacing event delivery
through the interrupt descriptor table (IDT event delivery) and event return by
the IRET instruction with lower latency transitions.
2) Improve software robustness by ensuring that event delivery establishes the
full supervisor context and that event return establishes the full user context.

The new transitions defined by the FRED architecture are FRED event delivery and,
for returning from events, two FRED return instructions. FRED event delivery can
effect a transition from ring 3 to ring 0, but it is used also to deliver events
incident to ring 0. One FRED instruction (ERETU) effects a return from ring 0 to
ring 3, while the other (ERETS) returns while remaining in ring 0.

Search for the latest FRED spec in most search engines with this search pattern:

site:intel.com FRED (flexible return and event delivery) specification

As of now there is no publicly avaiable CPU supporting FRED, thus the Intel
Simics® Simulator is used as software development and testing vehicles. And
it can be downloaded from:
https://www.intel.com/content/www/us/en/developer/articles/tool/simics-simulator.html

To enable FRED, the Simics package 8112 QSP-CPU needs to be installed with CPU
model configured as:
$cpu_comp_class = "x86-experimental-fred"

Longer term, we should refactor common code shared by FRED and IDT into common
shared files, and contain IDT code using a new config CONFIG_X86_IDT.

Changes since v6:
* Add a comment to explain why it is safe to write to a previous FRED stack
frame. (Lai Jiangshan).
* Export fred_entrypoint_kernel(), required when kvm-intel built as a module.
* Reserve a REDZONE for CALL emulation and Align RSP to a 64-byte boundary
before pushing a new FRED stack frame.
* Replace pt_regs csx flags prefix FRED_CSL_ with FRED_CSX_.

Changes since v5:
* Initialize system_interrupt_handlers with dispatch_table_spurious_interrupt()
instead of NULL to get rid of a branch (Peter Zijlstra).
* Disallow #DB inside #MCE for robustness sake (Peter Zijlstra).
* Add a comment for FRED stack level settings (Lai Jiangshan).
* Move the NMI bit from an invalid stack frame, which caused ERETU to fault,
to the fault handler's stack frame, thus to unblock NMI ASAP if NMI is blocked
(Lai Jiangshan).
* Refactor VMX_DO_EVENT_IRQOFF to handle IRQ/NMI in IRQ/NMI induced VM exits
when FRED is enabled (Sean Christopherson).

Changes since v4:
* Do NOT use the term "injection", which in the KVM context means to
reinject an event into the guest (Sean Christopherson).
* Add the explanation of why to execute "int $2" to invoke the NMI handler
in NMI caused VM exits (Sean Christopherson).
* Use cs/ss instead of csx/ssx when initializing the pt_regs structure
for calling external_interrupt(), otherwise it breaks i386 build.

Changes since v3:
* Call external_interrupt() to handle IRQ in IRQ caused VM exits.
* Execute "int $2" to handle NMI in NMI caused VM exits.
* Rename csl/ssl of the pt_regs structure to csx/ssx (x for extended)
(Andrew Cooper).

Changes since v2:
* Improve comments for changes in arch/x86/include/asm/idtentry.h.

Changes since v1:
* call irqentry_nmi_{enter,exit}() in both IDT and FRED debug fault kernel
handler (Peter Zijlstra).
* 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).

H. Peter Anvin (Intel) (24):
x86/traps: let common_interrupt() handle IRQ_MOVE_CLEANUP_VECTOR
x86/fred: make unions for the cs and ss fields in struct pt_regs
x86/traps: add a system interrupt table for system interrupt dispatch
x86/traps: add external_interrupt() to dispatch external interrupts
x86/cpufeature: add the cpu feature bit for FRED
x86/opcode: add ERETU, ERETS instructions to x86-opcode-map
x86/objtool: teach objtool about ERETU and ERETS
x86/cpu: add X86_CR4_FRED macro
x86/fred: add Kconfig option for FRED (CONFIG_X86_FRED)
x86/fred: if CONFIG_X86_FRED is disabled, disable FRED support
x86/cpu: add MSR numbers for FRED configuration
x86/fred: header file with FRED definitions
x86/fred: reserve space for the FRED stack frame
x86/fred: add a page fault entry stub for FRED
x86/fred: add a debug fault entry stub for FRED
x86/fred: add a NMI entry stub for FRED
x86/fred: FRED entry/exit and dispatch code
x86/fred: FRED initialization code
x86/fred: update MSR_IA32_FRED_RSP0 during task switch
x86/fred: let ret_from_fork() jmp to fred_exit_user when FRED is
enabled
x86/fred: disallow the swapgs instruction when FRED is enabled
x86/fred: no ESPFIX needed when FRED is enabled
x86/fred: allow single-step trap and NMI when starting a new thread
x86/fred: allow FRED systems to use interrupt vectors 0x10-0x1f

Xin Li (9):
x86/traps: add install_system_interrupt_handler()
x86/fred: header file for event types
x86/fred: add a machine check entry stub for FRED
x86/fred: fixup fault on ERETU by jumping to fred_entrypoint_user
x86/ia32: do not modify the DPL bits for a null selector
x86/fred: allow dynamic stack frame size
x86/fred: BUG() when ERETU with %rsp not equal to that when the ring 3
event was just delivered
x86/fred: disable FRED by default in its early stage
KVM: x86/vmx: refactor VMX_DO_EVENT_IRQOFF to generate FRED stack
frames

.../admin-guide/kernel-parameters.txt | 4 +
arch/x86/Kconfig | 9 +
arch/x86/entry/Makefile | 5 +-
arch/x86/entry/entry_32.S | 2 +-
arch/x86/entry/entry_64.S | 5 +
arch/x86/entry/entry_64_fred.S | 62 +++++
arch/x86/entry/entry_fred.c | 222 ++++++++++++++++++
arch/x86/entry/vsyscall/vsyscall_64.c | 2 +-
arch/x86/include/asm/asm-prototypes.h | 1 +
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/disabled-features.h | 8 +-
arch/x86/include/asm/entry-common.h | 3 +
arch/x86/include/asm/event-type.h | 17 ++
arch/x86/include/asm/extable_fixup_types.h | 4 +-
arch/x86/include/asm/fred.h | 150 ++++++++++++
arch/x86/include/asm/idtentry.h | 76 +++++-
arch/x86/include/asm/irq.h | 5 +
arch/x86/include/asm/irq_vectors.h | 15 +-
arch/x86/include/asm/msr-index.h | 13 +-
arch/x86/include/asm/processor.h | 12 +-
arch/x86/include/asm/ptrace.h | 34 ++-
arch/x86/include/asm/switch_to.h | 10 +-
arch/x86/include/asm/thread_info.h | 35 +--
arch/x86/include/asm/traps.h | 13 +
arch/x86/include/asm/vmx.h | 17 +-
arch/x86/include/uapi/asm/processor-flags.h | 2 +
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/apic/apic.c | 11 +-
arch/x86/kernel/apic/vector.c | 8 +-
arch/x86/kernel/cpu/acrn.c | 7 +-
arch/x86/kernel/cpu/common.c | 88 ++++---
arch/x86/kernel/cpu/mce/core.c | 15 ++
arch/x86/kernel/cpu/mshyperv.c | 22 +-
arch/x86/kernel/espfix_64.c | 8 +
arch/x86/kernel/fred.c | 78 ++++++
arch/x86/kernel/head_32.S | 3 +-
arch/x86/kernel/idt.c | 6 +-
arch/x86/kernel/irq.c | 6 +-
arch/x86/kernel/irqinit.c | 7 +-
arch/x86/kernel/kvm.c | 4 +-
arch/x86/kernel/nmi.c | 19 ++
arch/x86/kernel/process.c | 5 +
arch/x86/kernel/process_64.c | 21 +-
arch/x86/kernel/signal_32.c | 21 +-
arch/x86/kernel/traps.c | 175 ++++++++++++--
arch/x86/kvm/vmx/vmenter.S | 74 +++++-
arch/x86/kvm/vmx/vmx.c | 16 +-
arch/x86/lib/x86-opcode-map.txt | 2 +-
arch/x86/mm/extable.c | 84 +++++++
arch/x86/mm/fault.c | 20 +-
drivers/xen/events/events_base.c | 5 +-
kernel/fork.c | 6 +
tools/arch/x86/include/asm/cpufeatures.h | 1 +
.../arch/x86/include/asm/disabled-features.h | 8 +-
tools/arch/x86/include/asm/msr-index.h | 13 +-
tools/arch/x86/lib/x86-opcode-map.txt | 2 +-
tools/objtool/arch/x86/decode.c | 19 +-
57 files changed, 1306 insertions(+), 176 deletions(-)
create mode 100644 arch/x86/entry/entry_64_fred.S
create mode 100644 arch/x86/entry/entry_fred.c
create mode 100644 arch/x86/include/asm/event-type.h
create mode 100644 arch/x86/include/asm/fred.h
create mode 100644 arch/x86/kernel/fred.c

--
2.34.1