Re: [EXT] Re: SEV-SNP: Prepare for SNP page validation 1/4

Mark Kettenis <[email protected]>
Newsgroups gmane.os.openbsd.tech
Message-ID <[email protected]> 
> Date: Tue, 18 Aug 2026 13:22:00 +0200
> From: Hans-Jörg Höxer <[email protected]>
> 
> On Mon, Aug 17, 2026 at 09:50:51AM -0600, Theo de Raadt wrote:
> > Looks good.  Did you see any code which can move so that one #ifdef
> > covers two chunks?
> > 
> 
> in locore0 I could move a chunk around and save one #ifdef.  Updated diff
> below.
> 
> ok?

looks good to me

> 
> Take care,
> HJ.
> -----------------------
> Subject: SEV: Add option AMDSEV
> 
> To allow building the small RAMDISK kernel without SEV-* support
> introduce the option AMDSEV.
> 
> When running a non-SEV kernel as a SEV guest we will raise a #VC
> exception on the very first CPUID instruction.  To allow a somehwat
> graceful termination keep the locore0 #VC trap handler, fall through
> to the termination code and issue  TERMINATION request to the
> hypervisor.  In all other environments #VC will never be raised and
> the kernel runs normally.
> 
> Build RAMDISK without SEV-* support, all other kernel keep SEV-*
> support.
> 
> While there, cleanup and unify some definitions of the MSR protocol.
> ---
>  sys/arch/amd64/amd64/bus_space.c   |  7 +++++++
>  sys/arch/amd64/amd64/locore0.S     | 27 +++++++++++++++------------
>  sys/arch/amd64/amd64/machdep.c     |  4 ++++
>  sys/arch/amd64/amd64/trap.c        |  8 ++++++++
>  sys/arch/amd64/amd64/vector.S      |  6 ++++++
>  sys/arch/amd64/amd64/vmm_machdep.c |  2 +-
>  sys/arch/amd64/conf/GENERIC        |  1 +
>  sys/arch/amd64/conf/RAMDISK_CD     |  1 +
>  sys/arch/amd64/conf/VMBOOT         |  1 +
>  sys/arch/amd64/conf/files.amd64    |  4 ++--
>  sys/arch/amd64/include/ghcb.h      | 30 ++++++++++++++++++++++--------
>  11 files changed, 68 insertions(+), 23 deletions(-)
> 
> diff --git a/sys/arch/amd64/amd64/bus_space.c b/sys/arch/amd64/amd64/bus_space.c
> index 9439ca6b954..376c64ed13c 100644
> --- a/sys/arch/amd64/amd64/bus_space.c
> +++ b/sys/arch/amd64/amd64/bus_space.c
> @@ -317,8 +317,10 @@ const struct x86_bus_space_ops default_bus_space_mem_ops = {
>  
>  const struct x86_bus_space_ops *x86_bus_space_mem_ops;
>  
> +#ifdef AMDSEV
>  extern const struct x86_bus_space_ops sev_ghcb_bus_space_io_ops;
>  extern const struct x86_bus_space_ops sev_ghcb_bus_space_mem_ops;
> +#endif
>  
>  void
>  x86_bus_space_init(void)
> @@ -341,6 +343,7 @@ x86_bus_space_init(void)
>  	    (caddr_t)iomem_ex_storage, sizeof(iomem_ex_storage),
>  	    EX_NOCOALESCE|EX_NOWAIT);
>  
> +#ifdef AMDSEV
>  	if (ISSET(cpu_sev_guestmode, SEV_STAT_ES_ENABLED)) {
>  		x86_bus_space_mem_ops = &sev_ghcb_bus_space_mem_ops;
>  		x86_bus_space_io_ops  = &sev_ghcb_bus_space_io_ops;
> @@ -348,6 +351,10 @@ x86_bus_space_init(void)
>  		x86_bus_space_mem_ops = &default_bus_space_mem_ops;
>  		x86_bus_space_io_ops  = &default_bus_space_io_ops;
>  	}
> +#else
> +	x86_bus_space_mem_ops = &default_bus_space_mem_ops;
> +	x86_bus_space_io_ops  = &default_bus_space_io_ops;
> +#endif
>  }
>  
>  void
> diff --git a/sys/arch/amd64/amd64/locore0.S b/sys/arch/amd64/amd64/locore0.S
> index f8ba97805ce..d0466ab82e1 100644
> --- a/sys/arch/amd64/amd64/locore0.S
> +++ b/sys/arch/amd64/amd64/locore0.S
> @@ -810,19 +810,9 @@ longmode_hi:
>  	call	main
>  
>  	.code32
> -vc_cpuid32:
> -	shll	$30, %eax		/* requested register */
> -	orl	$MSR_PROTO_CPUID_REQ, %eax
> -	movl	%ebx, %edx		/* CPUID function */
> -	movl	$MSR_SEV_GHCB, %ecx
> -	wrmsr
> -	rep vmmcall
> -	rdmsr
> -	ret
> -	lfence
> -
>  	.globl	locore_vc_trap32
>  locore_vc_trap32:
> +#ifdef AMDSEV
>  	pushl	%eax
>  	pushl	%ebx
>  	pushl	%ecx
> @@ -871,8 +861,21 @@ locore_vc_trap32:
>  	addl	$3, (%esp)		/* skip mov,%db */
>  	iret
>  
> +vc_cpuid32:
> +	shll	$30, %eax		/* requested register */
> +	orl	$MSR_PROTO_CPUID_REQ, %eax
> +	movl	%ebx, %edx		/* CPUID function */
> +	movl	$MSR_SEV_GHCB, %ecx
> +	wrmsr
> +	rep vmmcall
> +	rdmsr
> +	ret
> +	lfence
> +#endif	/* AMDSEV */
> +	/* !AMDSEV: FALLTHROUGH and graceful termination */
> +
>  .Lterminate32:
> -	movl	$MSR_PROTO_TERMINATE, %eax
> +	movl	$MSR_PROTO_TERMINATION_REQ, %eax
>  	movl	$MSR_SEV_GHCB, %ecx
>  	wrmsr
>  	rep vmmcall
> diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
> index bbf1e415962..6891733bd24 100644
> --- a/sys/arch/amd64/amd64/machdep.c
> +++ b/sys/arch/amd64/amd64/machdep.c
> @@ -1335,6 +1335,7 @@ cpu_init_idt(void)
>  	lidt(&region);
>  }
>  
> +#ifdef AMDSEV
>  uint64_t early_gdt[GDT_SIZE / 8];
>  
>  void
> @@ -1366,6 +1367,7 @@ cpu_init_early_vctrap(paddr_t addr)
>  	memset((void *)ghcb_vaddr, 0, 2 * PAGE_SIZE);
>  	wrmsr(MSR_SEV_GHCB, ghcb_paddr);
>  }
> +#endif	/* AMDSEV */
>  
>  void
>  cpu_init_extents(void)
> @@ -1494,6 +1496,7 @@ init_x86_64(paddr_t first_avail)
>  	    ((pmap_direct_rand & DIRECT_MAP_START_MASK) * NBPD_L4))));
>  	pmap_direct_end = pmap_direct_base + DIRECT_MAP_SIZE;
>  
> +#ifdef AMDSEV
>  	/*
>  	 * locore0 mapped 2 pages for use as GHCB before pmap is initialized.
>  	 */
> @@ -1503,6 +1506,7 @@ init_x86_64(paddr_t first_avail)
>  	}
>  	if (ISSET(cpu_sev_guestmode, SEV_STAT_ENABLED))
>  		boothowto |= RB_COCOVM;
> +#endif
>  
>  	/*
>  	 * locore0 mapped 3 pages for use before the pmap is initialized
> diff --git a/sys/arch/amd64/amd64/trap.c b/sys/arch/amd64/amd64/trap.c
> index ccd0315186c..95d57b59f5a 100644
> --- a/sys/arch/amd64/amd64/trap.c
> +++ b/sys/arch/amd64/amd64/trap.c
> @@ -97,7 +97,9 @@
>  
>  int	upageflttrap(struct trapframe *, uint64_t);
>  int	kpageflttrap(struct trapframe *, uint64_t);
> +#ifdef AMDSEV
>  int	vctrap(struct trapframe *, int, int *, int *);
> +#endif
>  void	kerntrap(struct trapframe *);
>  void	usertrap(struct trapframe *);
>  void	ast(struct trapframe *);
> @@ -301,6 +303,7 @@ kpageflttrap(struct trapframe *frame, uint64_t cr2)
>  	return 1;
>  }
>  
> +#ifdef AMDSEV
>  int
>  vctrap(struct trapframe *frame, int user, int *sig, int *code)
>  {
> @@ -492,6 +495,7 @@ vctrap(struct trapframe *frame, int user, int *sig, int *code)
>  
>  	return 1;
>  }
> +#endif	/* AMDSEV */
>  
>  
>  /*
> @@ -545,10 +549,12 @@ kerntrap(struct trapframe *frame)
>  			return;
>  #endif /* NISA > 0 */
>  
> +#ifdef AMDSEV
>  	case T_VC:
>  		if (vctrap(frame, 0, NULL, NULL))
>  			return;
>  		goto we_re_toast;
> +#endif
>  	}
>  }
>  
> @@ -628,10 +634,12 @@ usertrap(struct trapframe *frame)
>  		code = (frame->tf_err & 0x7fff) < 4 ? ILL_BTCFI
>  		    : ILL_BADSTK;
>  		break;
> +#ifdef AMDSEV
>  	case T_VC:
>  		if (vctrap(frame, 1, &sig, &code))
>  			goto out;
>  		break;
> +#endif
>  	case T_PAGEFLT:			/* page fault */
>  		if (!uvm_map_inentry(p, &p->p_spinentry, PROC_STACK(p),
>  		    "[%s]%d/%d sp=%lx inside %lx-%lx: not MAP_STACK\n",
> diff --git a/sys/arch/amd64/amd64/vector.S b/sys/arch/amd64/amd64/vector.S
> index 9de0ee97f08..354f29a06a3 100644
> --- a/sys/arch/amd64/amd64/vector.S
> +++ b/sys/arch/amd64/amd64/vector.S
> @@ -375,6 +375,7 @@ IDTVEC(trap14)
>  IDTVEC(trap15)
>  	TRAP(T_CP)
>  
> +#ifdef AMDSEV
>  IDTVEC(trap1d)
>  	/*
>  	 * #VC is AMD CPU specific, thus we don't use any Intel Meltdown
> @@ -408,6 +409,9 @@ vctrap_kern:
>  	SMAP_CLAC
>  	/* shortcut to regular path, but with interrupts disabled */
>  	jmp	.Lreal_kern_trap
> +#else
> +IDTVEC_ALIAS(trap1d, trap1f)
> +#endif	/* AMDSEV */
>  
>  IDTVEC(trap1f)
>  IDTVEC_ALIAS(trap16, trap1f)
> @@ -548,6 +552,7 @@ END(alltraps_kern)
>  END(alltraps_kern_meltdown)
>  KTEXT_PAGE_END
>  
> +#ifdef AMDSEV
>  /* #VC trap entry for early bootstrap */
>  IDTVEC(vctrap_early)
>  	pushq	$T_VC
> @@ -558,6 +563,7 @@ IDTVEC(vctrap_early)
>  	call	vctrap
>  	movq	$0,-8(%rsp)
>  	INTRFASTEXIT
> +#endif
>  
>  /*
>   * Macros for interrupt entry, call to handler, and exit.
> diff --git a/sys/arch/amd64/amd64/vmm_machdep.c b/sys/arch/amd64/amd64/vmm_machdep.c
> index 787b65e29e1..850010abb90 100644
> --- a/sys/arch/amd64/amd64/vmm_machdep.c
> +++ b/sys/arch/amd64/amd64/vmm_machdep.c
> @@ -4523,7 +4523,7 @@ svm_handle_vmgexit(struct vcpu *vcpu)
>  		req = (vmcb->v_ghcb_gpa & 0xffffffff);
>  
>  		/* We only support cpuid and terminate. */
> -		if ((req & ~PG_FRAME) == MSR_PROTO_TERMINATE) {
> +		if ((req & ~PG_FRAME) == MSR_PROTO_TERMINATION_REQ) {
>  			DPRINTF("%s: guest requests termination\n", __func__);
>  			return (1);
>  		} else if ((req & ~PG_FRAME) != MSR_PROTO_CPUID_REQ)
> diff --git a/sys/arch/amd64/conf/GENERIC b/sys/arch/amd64/conf/GENERIC
> index c3680e2fb21..fe6a8c62f6f 100644
> --- a/sys/arch/amd64/conf/GENERIC
> +++ b/sys/arch/amd64/conf/GENERIC
> @@ -21,6 +21,7 @@ option		MTRR		# CPU memory range attributes control
>  option		NTFS		# NTFS support
>  option		SUSPEND
>  option		HIBERNATE
> +option		AMDSEV
>  
>  config		bsd	swap generic
>  
> diff --git a/sys/arch/amd64/conf/RAMDISK_CD b/sys/arch/amd64/conf/RAMDISK_CD
> index 82cf1b89a25..b7ee25adef0 100644
> --- a/sys/arch/amd64/conf/RAMDISK_CD
> +++ b/sys/arch/amd64/conf/RAMDISK_CD
> @@ -19,6 +19,7 @@ option		UDF
>  option		MSDOSFS
>  option		INET6
>  option		CRYPTO
> +option		AMDSEV
>  
>  option		FONT_SPLEEN8x16
>  option		FONT_SPLEEN12x24
> diff --git a/sys/arch/amd64/conf/VMBOOT b/sys/arch/amd64/conf/VMBOOT
> index 5a615b98288..68ba0d7773b 100644
> --- a/sys/arch/amd64/conf/VMBOOT
> +++ b/sys/arch/amd64/conf/VMBOOT
> @@ -7,6 +7,7 @@ option		BOOT_KERNEL
>  option		SMALL_KERNEL
>  option		NO_PROPOLICE
>  option		BOOT_CONFIG
> +option		AMDSEV
>  
>  option		RAMDISK_HOOKS
>  option		MINIROOTSIZE=4480
> diff --git a/sys/arch/amd64/conf/files.amd64 b/sys/arch/amd64/conf/files.amd64
> index 0c1e224f5c2..ebd75315eb8 100644
> --- a/sys/arch/amd64/conf/files.amd64
> +++ b/sys/arch/amd64/conf/files.amd64
> @@ -28,8 +28,8 @@ file	arch/amd64/amd64/vm_machdep.c
>  file	arch/amd64/amd64/fpu.c
>  file	arch/amd64/amd64/i8259.c
>  file	arch/amd64/amd64/cacheinfo.c
> -file	arch/amd64/amd64/ghcb.c
> -file	arch/amd64/amd64/sev_bus_space.c
> +file	arch/amd64/amd64/ghcb.c			amdsev
> +file	arch/amd64/amd64/sev_bus_space.c	amdsev
>  file	arch/amd64/amd64/vector.S
>  file	arch/amd64/amd64/copy.S
>  file	arch/amd64/amd64/spl.S
> diff --git a/sys/arch/amd64/include/ghcb.h b/sys/arch/amd64/include/ghcb.h
> index 55e184186ab..104e36dda87 100644
> --- a/sys/arch/amd64/include/ghcb.h
> +++ b/sys/arch/amd64/include/ghcb.h
> @@ -19,6 +19,8 @@
>  #ifndef _MACHINE_GHCB_H_
>  #define _MACHINE_GHCB_H_
>  
> +#ifdef AMDSEV
> +
>  #ifndef _LOCORE
>  
>  #include <sys/systm.h>
> @@ -42,6 +44,19 @@
>  
>  #define GHCB_MAX			0xFFF
>  
> +#endif	/* !_LOCORE */
> +
> +/* Definitions used with the MSR protocol */
> +#define MSR_PROTO_CPUID_REQ			0x4
> +#define MSR_PROTO_CPUID_RESP			0x5
> +#define MSR_PROTO_PREFERRED_GHCB_PA_REQ		0x10
> +#define MSR_PROTO_PREFERRED_GHCB_PA_RESP	0x11
> +#define MSR_PROTO_REGISTER_GHCB_PA_REQ		0x12
> +#define MSR_PROTO_REGISTER_GHCB_PA_RESP		0x13
> +#define MSR_PROTO_TERMINATION_REQ		0x100
> +
> +#ifndef _LOCORE
> +
>  struct ghcb_sa {
>  	uint8_t			v_pad0[0xcb];		/* 000h-0CAh */
>  	uint8_t			v_cpl;			/* 0CBh */
> @@ -102,14 +117,6 @@ struct ghcb_sync {
>  	int			sz_c;
>  	int			sz_d;
>  };
> -#endif /* !_LOCORE */
> -
> -/* Definitions used with the MSR protocol */
> -#define MSR_PROTO_CPUID_REQ	0x4
> -#define MSR_PROTO_CPUID_RESP	0x5
> -#define MSR_PROTO_TERMINATE	0x100
> -
> -#ifndef _LOCORE
>  
>  extern vaddr_t ghcb_vaddr;
>  extern paddr_t ghcb_paddr;
> @@ -249,4 +256,11 @@ ghcb_io_write_4(uint16_t port, uint32_t v)
>  
>  #endif /* !_LOCORE */
>  
> +#else	/* !AMDSEV */
> +
> +/* Definitions used with the MSR protocol */
> +#define MSR_PROTO_TERMINATION_REQ		0x100
> +
> +#endif	/* AMDSEV */
> +
>  #endif /* !_MACHINE_GHCB_H_ */
> -- 
> 2.53.0
> 
> 
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>
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