x86/entry: Add fred_entry_from_kvm() for VMX to handle IRQ/NMI

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@google.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-32-xin3.li@intel.com

diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S
index 7fe2722ad90c16fe238a27b367081680fca34594..a02bc6f3d2e6a43d4e00c4657986382029065aa0 100644 (file)
--- a/arch/x86/entry/entry_64_fred.S
+++ b/arch/x86/entry/entry_64_fred.S
@@ -3,8 +3,11 @@
  * The actual FRED entry points.
  */
 
+#include <linux/export.h>
+
 #include <asm/asm.h>
 #include <asm/fred.h>
+#include <asm/segment.h>
 
 #include "calling.h"
 
@@ -52,3 +55,77 @@ 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
+
+       UNWIND_HINT_SAVE
+
+       /*
+        * Both IRQ and NMI from VMX can be handled on current task stack
+        * because there is no need to protect from reentrancy and the call
+        * stack leading to this helper is effectively constant and shallow
+        * (relatively speaking). Do the same when FRED is active, i.e., no
+        * need to check current stack level for a stack switch.
+        *
+        * 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
+       RET
+
+SYM_FUNC_END(asm_fred_entry_from_kvm)
+EXPORT_SYMBOL_GPL(asm_fred_entry_from_kvm);
+#endif

diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c
index 3be0269bc0d465857da3b95308a78b3854ac03d9..6ecc08b6d72a24b2f24dca95279678e67e55868f 100644 (file)
--- a/arch/x86/entry/entry_fred.c
+++ b/arch/x86/entry/entry_fred.c
@@ -257,3 +257,17 @@ __visible noinstr void fred_entry_from_kernel(struct pt_regs *regs)
 
        return fred_bad_type(regs, error_code);
 }
+
+#if IS_ENABLED(CONFIG_KVM_INTEL)
+__visible noinstr void __fred_entry_from_kvm(struct pt_regs *regs)
+{
+       switch (regs->fred_ss.type) {
+       case EVENT_TYPE_EXTINT:
+               return fred_extint(regs);
+       case EVENT_TYPE_NMI:
+               return fred_exc_nmi(regs);
+       default:
+               WARN_ON_ONCE(1);
+       }
+}
+#endif

diff --git a/arch/x86/include/asm/fred.h b/arch/x86/include/asm/fred.h
index 16a64ffecbf8d5512a7c3247b81900e2f5523dd3..2fa9f34e5c95f5c18db8e8181d6521c502c022f6 100644 (file)
--- a/arch/x86/include/asm/fred.h
+++ b/arch/x86/include/asm/fred.h
@@ -9,6 +9,7 @@
 #include <linux/const.h>
 
 #include <asm/asm.h>
+#include <asm/trapnr.h>
 
 /*
  * FRED event return instruction opcodes for ERET{S,U}; supported in
@@ -62,12 +63,29 @@ static __always_inline unsigned long fred_event_data(struct pt_regs *regs)
 
 void asm_fred_entrypoint_user(void);
 void asm_fred_entrypoint_kernel(void);
+void asm_fred_entry_from_kvm(struct fred_ss);
 
 __visible void fred_entry_from_user(struct pt_regs *regs);
 __visible void fred_entry_from_kernel(struct pt_regs *regs);
+__visible void __fred_entry_from_kvm(struct pt_regs *regs);
+
+/* Can be called from noinstr code, thus __always_inline */
+static __always_inline void fred_entry_from_kvm(unsigned int type, unsigned int vector)
+{
+       struct fred_ss ss = {
+               .ss     =__KERNEL_DS,
+               .type   = type,
+               .vector = vector,
+               .nmi    = type == EVENT_TYPE_NMI,
+               .lm     = 1,
+       };
+
+       asm_fred_entry_from_kvm(ss);
+}
 
 #else /* CONFIG_X86_FRED */
 static __always_inline unsigned long fred_event_data(struct pt_regs *regs) { return 0; }
+static __always_inline void fred_entry_from_kvm(unsigned int type, unsigned int vector) { }
 #endif /* CONFIG_X86_FRED */
 #endif /* !__ASSEMBLY__ */