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diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -1830,6 +1830,56 @@
: "cc", "memory");
}
+extern const char wrmsr_early_safe_gp_handler[];
+static uint64_t orig_gp_handler;
+
+static struct gate_descriptor *
+wrmsr_early_get_gp_descr(void)
+{
+ struct region_descriptor efi_idt;
+ struct gate_descriptor *gpf_descr;
+
+ lidt(&efi_idt);
+ return ((void *)(uintptr_t)(efi_idt.rd_base +
+ sizeof(*gpf_descr) * IDT_GP));
+}
+
+static void
+wrmsr_early_set_gp_handler(uint64_t h)
+{
+ struct gate_descriptor *gpf_descr;
+
+ gpf_descr = wrmsr_early_get_gp_descr();
+ gpf_descr->gd_looffset = h;
+ gpf_descr->gd_hioffset = h >> 16;
+}
+
+static uint64_t
+wrmsr_early_get_gp_handler(void)
+{
+ struct gate_descriptor *gpf_descr;
+ uint64_t res;
+
+ gpf_descr = wrmsr_early_get_gp_descr();
+ res = gpf_descr->gd_hioffset;
+ res <<= 16;
+ res |= gpf_descr->gd_looffset;
+ return (res);
+}
+
+void
+wrmsr_early_safe_start(void)
+{
+ orig_gp_handler = wrmsr_early_get_gp_handler();
+ wrmsr_early_set_gp_handler((uintptr_t)wrmsr_early_safe_gp_handler);
+}
+
+void
+wrmsr_early_safe_end(void)
+{
+ wrmsr_early_set_gp_handler(orig_gp_handler);
+}
+
#ifdef KDB
/*
diff --git a/sys/amd64/amd64/support.S b/sys/amd64/amd64/support.S
--- a/sys/amd64/amd64/support.S
+++ b/sys/amd64/amd64/support.S
@@ -1565,6 +1565,25 @@
POP_FRAME_POINTER
ret
+ENTRY(wrmsr_early_safe)
+ movl %edi,%ecx
+ movl %esi,%eax
+ sarq $32,%rsi
+ movl %esi,%edx
+wrmsrF: wrmsr
+ xorl %eax,%eax
+ POP_FRAME_POINTER
+ ret
+
+ENTRY(wrmsr_early_faulted)
+ movl $EFAULT,%eax
+ POP_FRAME_POINTER
+ ret
+
+ENTRY(wrmsr_early_safe_gp_handler)
+ movq $wrmsr_early_faulted,8(%rsp)
+ iretq
+
/*
* void pmap_pti_pcid_invalidate(uint64_t ucr3, uint64_t kcr3);
* Invalidates address space addressed by ucr3, then returns to kcr3.
diff --git a/sys/amd64/include/md_var.h b/sys/amd64/include/md_var.h
--- a/sys/amd64/include/md_var.h
+++ b/sys/amd64/include/md_var.h
@@ -100,6 +100,10 @@
int set_fpcontext(struct thread *td, struct __mcontext *mcp,
char *xfpustate, size_t xfpustate_len);
+void wrmsr_early_safe_start(void);
+void wrmsr_early_safe_end(void);
+int wrmsr_early_safe(u_int msr, uint64_t data);
+
#endif /* !_MACHINE_MD_VAR_H_ */
#endif /* __i386__ */

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