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This patch set enables the Intel flexible return and event delivery
(FRED) architecture for x86-64.
The 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. Collectively, FRED
event delivery and the FRED return instructions are FRED transitions.
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"
Changes since v8:
* Move the FRED initialization patch after all required changes are in
place (Thomas Gleixner).
* 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).
* Introduce a macro sysvec_install() to derive the asm handler name from
a C handler, which simplifies the code and avoids an ugly typecast
(Thomas Gleixner).
* Remove junk code that assumes no local APIC on x86_64 (Thomas Gleixner).
* Put IDTENTRY changes in a separate patch (Thomas Gleixner).
* Use high-order 48 bits above the lowest 16 bit SS only when FRED is
enabled (Thomas Gleixner).
* Explain why writing directly to the IA32_KERNEL_GS_BASE MSR is
doing the right thing (Thomas Gleixner).
* Reword some patch descriptions (Thomas Gleixner).
* Add a new macro VMX_DO_FRED_EVENT_IRQOFF for FRED instead of
refactoring VMX_DO_EVENT_IRQOFF (Sean Christopherson).
* Do NOT use a trampoline, just LEA+PUSH the return RIP, PUSH the error
code, and jump to the FRED kernel entry point for NMI or call
external_interrupt() for IRQs (Sean Christopherson).
* Call external_interrupt() only when FRED is enabled, and convert the
non-FRED handling to external_interrupt() after FRED lands (Sean
Christopherson).
* Use __packed instead of __attribute__((__packed__)) (Borislav Petkov).
* Put all comments above the members, like the rest of the file does
(Borislav Petkov).
* Reflect the FRED spec 5.0 change that ERETS and ERETU add 8 to %rsp
before popping the return context from the stack.
* Reflect stack frame definition changes from FRED spec 3.0 to 5.0.
* Add ENDBR to the FRED_ENTER asm macro after kernel IBT is added to
FRED base line in FRED spec 5.0.
* Add a document which briefly introduces FRED features.
* Remove 2 patches, "allow FRED systems to use interrupt vectors
0x10-0x1f" and "allow dynamic stack frame size", from this patch set,
as they are "optimizations" only.
* Send 2 patches, "header file for event types" and "do not modify the
DPL bits for a null selector", as pre-FRED patches.
Changes since v7:
* Always call external_interrupt() for VMX IRQ handling on x86_64, thus avoid
re-entering the noinstr code.
* Create a FRED stack frame when FRED is compiled-in but not enabled, which
uses some extra stack space but simplifies the code.
* Add a log message when FRED is enabled.
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) (22):
x86/fred: Add Kconfig option for FRED (CONFIG_X86_FRED)
x86/fred: Disable FRED support if CONFIG_X86_FRED is disabled
x86/cpufeatures: 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/cpu: Add MSR numbers for FRED configuration
x86/fred: Make unions for the cs and ss fields in struct pt_regs
x86/fred: Add a new header file for FRED definitions
x86/fred: Reserve space for the FRED stack frame
x86/fred: Update MSR_IA32_FRED_RSP0 during task switch
x86/fred: Let ret_from_fork_asm() 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 task
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/traps: Add a system interrupt handler table for system interrupt
dispatch
x86/traps: Add external_interrupt() to dispatch external interrupts
x86/fred: FRED entry/exit and dispatch code
x86/fred: FRED initialization code
Xin Li (14):
Documentation/x86/64: Add documentation for FRED
x86/fred: Define a common function type fred_handler
x86/fred: Add a machine check entry stub for FRED
x86/fred: Add a double fault entry stub for FRED
x86/entry: Remove idtentry_sysvec from entry_{32,64}.S
x86/idtentry: Incorporate definitions/declarations of the FRED
external interrupt handler type
x86/traps: Add sysvec_install() to install a system interrupt handler
x86/idtentry: Incorporate declaration/definition of the FRED exception
handler type
x86/fred: Fixup fault on ERETU by jumping to fred_entrypoint_user
x86/traps: Export external_interrupt() for handling IRQ in IRQ induced
VM exits
x86/fred: Export fred_entrypoint_kernel() for handling NMI in NMI
induced VM exits
KVM: VMX: Add VMX_DO_FRED_EVENT_IRQOFF for IRQ/NMI handling
x86/syscall: Split IDT syscall setup code into idt_syscall_init()
x86/fred: Disable FRED by default in its early stage
.../admin-guide/kernel-parameters.txt | 4 +
Documentation/arch/x86/x86_64/fred.rst | 102 ++++++++
Documentation/arch/x86/x86_64/index.rst | 1 +
arch/x86/Kconfig | 9 +
arch/x86/entry/Makefile | 5 +-
arch/x86/entry/entry_32.S | 4 -
arch/x86/entry/entry_64.S | 14 +-
arch/x86/entry/entry_64_fred.S | 58 +++++
arch/x86/entry/entry_fred.c | 220 ++++++++++++++++++
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/extable_fixup_types.h | 4 +-
arch/x86/include/asm/fred.h | 157 +++++++++++++
arch/x86/include/asm/idtentry.h | 115 ++++++++-
arch/x86/include/asm/msr-index.h | 13 +-
arch/x86/include/asm/ptrace.h | 57 ++++-
arch/x86/include/asm/switch_to.h | 11 +-
arch/x86/include/asm/thread_info.h | 12 +-
arch/x86/include/asm/traps.h | 23 ++
arch/x86/include/uapi/asm/processor-flags.h | 2 +
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/cpu/acrn.c | 5 +-
arch/x86/kernel/cpu/common.c | 47 +++-
arch/x86/kernel/cpu/mce/core.c | 15 ++
arch/x86/kernel/cpu/mshyperv.c | 16 +-
arch/x86/kernel/espfix_64.c | 8 +
arch/x86/kernel/fred.c | 67 ++++++
arch/x86/kernel/irqinit.c | 7 +-
arch/x86/kernel/kvm.c | 2 +-
arch/x86/kernel/nmi.c | 19 ++
arch/x86/kernel/process_64.c | 31 ++-
arch/x86/kernel/traps.c | 153 ++++++++++--
arch/x86/kvm/vmx/vmenter.S | 88 +++++++
arch/x86/kvm/vmx/vmx.c | 19 +-
arch/x86/lib/x86-opcode-map.txt | 2 +-
arch/x86/mm/extable.c | 79 +++++++
arch/x86/mm/fault.c | 18 +-
drivers/xen/events/events_base.c | 3 +-
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 +-
45 files changed, 1348 insertions(+), 98 deletions(-)
create mode 100644 Documentation/arch/x86/x86_64/fred.rst
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/fred.h
create mode 100644 arch/x86/kernel/fred.c
--
2.34.1