Re: [PATCH v10 33/38] x86/entry: Add fred_entry_from_kvm() for VMX to handle IRQ/NMI

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On 14.09.23 г. 7:48 ч., Xin Li wrote:
In IRQ/NMI induced VM exits, KVM VMX needs to execute the respective
handlers, which requires the software to create a FRED stack frame,
and use it to invoke the handlers. Add fred_irq_entry_from_kvm() for
this job.

Export fred_entry_from_kvm() because VMX can be compiled as a module.

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---

Changes since v9:
* Shove the whole thing into arch/x86/entry/entry_64_fred.S for invoking
   external_interrupt() and fred_exc_nmi() (Sean Christopherson).
* Correct and improve a few comments (Sean Christopherson).
* Merge the two IRQ/NMI asm entries into one as it's fine to invoke
   noinstr code from regular code (Thomas Gleixner).
* Setup the long mode and NMI flags in the augmented SS field of FRED
   stack frame in C instead of asm (Thomas Gleixner).
* Add UNWIND_HINT_{SAVE,RESTORE} to get rid of the warning: "objtool:
   asm_fred_entry_from_kvm+0x0: unreachable instruction" (Peter Zijlstra).

Changes since v8:
* 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).
---
  arch/x86/entry/entry_64_fred.S | 73 ++++++++++++++++++++++++++++++++++
  arch/x86/entry/entry_fred.c    | 14 +++++++
  arch/x86/include/asm/fred.h    | 18 +++++++++
  3 files changed, 105 insertions(+)

diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S
index d1c2fc4af8ae..f1088d6f2054 100644
--- a/arch/x86/entry/entry_64_fred.S
+++ b/arch/x86/entry/entry_64_fred.S
@@ -4,7 +4,9 @@
   */
#include <asm/asm.h>
+#include <asm/export.h>
  #include <asm/fred.h>
+#include <asm/segment.h>
#include "calling.h" @@ -54,3 +56,74 @@ SYM_CODE_START_NOALIGN(asm_fred_entrypoint_kernel)
  	FRED_EXIT
  	ERETS
  SYM_CODE_END(asm_fred_entrypoint_kernel)
+
+#if IS_ENABLED(CONFIG_KVM_INTEL)
+SYM_FUNC_START(asm_fred_entry_from_kvm)
+	push %rbp
+	mov %rsp, %rbp

use FRAME_BEGIN/FRAME_END macros to ommit this code if CONFIG_FRAME_POINTER is disabled.

+
+	UNWIND_HINT_SAVE
+
+	/*
+	 * Don't check the FRED stack level, the call stack leading to this
+	 * helper is effectively constant and shallow (relatively speaking).
+	 *
+	 * Emulate the FRED-defined redzone and stack alignment.
+	 */
+	sub $(FRED_CONFIG_REDZONE_AMOUNT << 6), %rsp
+	and $FRED_STACK_FRAME_RSP_MASK, %rsp
+
+	/*
+	 * Start to push a FRED stack frame, which is always 64 bytes:
+	 *
+	 * +--------+-----------------+
+	 * | Bytes  | Usage           |
+	 * +--------+-----------------+
+	 * | 63:56  | Reserved        |
+	 * | 55:48  | Event Data      |
+	 * | 47:40  | SS + Event Info |
+	 * | 39:32  | RSP             |
+	 * | 31:24  | RFLAGS          |
+	 * | 23:16  | CS + Aux Info   |
+	 * |  15:8  | RIP             |
+	 * |   7:0  | Error Code      |
+	 * +--------+-----------------+
+	 */
+	push $0				/* Reserved, must be 0 */
+	push $0				/* Event data, 0 for IRQ/NMI */
+	push %rdi			/* fred_ss handed in by the caller */
+	push %rbp
+	pushf
+	mov $__KERNEL_CS, %rax
+	push %rax
+
+	/*
+	 * Unlike the IDT event delivery, FRED _always_ pushes an error code
+	 * after pushing the return RIP, thus the CALL instruction CANNOT be
+	 * used here to push the return RIP, otherwise there is no chance to
+	 * push an error code before invoking the IRQ/NMI handler.
+	 *
+	 * Use LEA to get the return RIP and push it, then push an error code.
+	 */
+	lea 1f(%rip), %rax
+	push %rax				/* Return RIP */
+	push $0					/* Error code, 0 for IRQ/NMI */
+
+	PUSH_AND_CLEAR_REGS clear_bp=0 unwind_hint=0
+	movq %rsp, %rdi				/* %rdi -> pt_regs */
+	call __fred_entry_from_kvm		/* Call the C entry point */
+	POP_REGS
+	ERETS
+1:
+	/*
+	 * Objtool doesn't understand what ERETS does, this hint tells it that
+	 * yes, we'll reach here and with what stack state. A save/restore pair
+	 * isn't strictly needed, but it's the simplest form.
+	 */
+	UNWIND_HINT_RESTORE
+	pop %rbp

FRAME_END

+	RET
+
+SYM_FUNC_END(asm_fred_entry_from_kvm)
+EXPORT_SYMBOL_GPL(asm_fred_entry_from_kvm);
+#endif


<snip>



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