mem_encrypt.S

/*
 * AMD Memory Encryption Support
 *
 * Copyright (C) 2017 Advanced Micro Devices, Inc.
 *
 * Author: Tom Lendacky <thomas.lendacky@amd.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/linkage.h>

#include <asm/processor-flags.h>
#include <asm/msr.h>
#include <asm/asm-offsets.h>

	.text
	.code32
ENTRY(get_sev_encryption_bit)
	xor	%eax, %eax

#ifdef CONFIG_AMD_MEM_ENCRYPT
	push	%ebx
	push	%ecx
	push	%edx
	push	%edi

	/*
	 * RIP-relative addressing is needed to access the encryption bit
	 * variable. Since we are running in 32-bit mode we need this call/pop
	 * sequence to get the proper relative addressing.
	 */
	call	1f
1:	popl	%edi
	subl	$1b, %edi

	movl	enc_bit(%edi), %eax
	cmpl	$0, %eax
	jge	.Lsev_exit

	/* Check if running under a hypervisor */
	movl	$1, %eax
	cpuid
	bt	$31, %ecx		/* Check the hypervisor bit */
	jnc	.Lno_sev

	movl	$0x80000000, %eax	/* CPUID to check the highest leaf */
	cpuid
	cmpl	$0x8000001f, %eax	/* See if 0x8000001f is available */
	jb	.Lno_sev

	/*
	 * Check for the SEV feature:
	 *   CPUID Fn8000_001F[EAX] - Bit 1
	 *   CPUID Fn8000_001F[EBX] - Bits 5:0
	 *     Pagetable bit position used to indicate encryption
	 */
	movl	$0x8000001f, %eax
	cpuid
	bt	$1, %eax		/* Check if SEV is available */
	jnc	.Lno_sev

	movl	$MSR_AMD64_SEV, %ecx	/* Read the SEV MSR */
	rdmsr
	bt	$MSR_AMD64_SEV_ENABLED_BIT, %eax	/* Check if SEV is active */
	jnc	.Lno_sev

	movl	%ebx, %eax
	andl	$0x3f, %eax		/* Return the encryption bit location */
	movl	%eax, enc_bit(%edi)
	jmp	.Lsev_exit

.Lno_sev:
	xor	%eax, %eax
	movl	%eax, enc_bit(%edi)

.Lsev_exit:
	pop	%edi
	pop	%edx
	pop	%ecx
	pop	%ebx

#endif	/* CONFIG_AMD_MEM_ENCRYPT */

	ret
ENDPROC(get_sev_encryption_bit)

	.code64
ENTRY(get_sev_encryption_mask)
	xor	%rax, %rax

#ifdef CONFIG_AMD_MEM_ENCRYPT
	push	%rbp
	push	%rdx

	movq	%rsp, %rbp		/* Save current stack pointer */

	call	get_sev_encryption_bit	/* Get the encryption bit position */
	testl	%eax, %eax
	jz	.Lno_sev_mask

	xor	%rdx, %rdx
	bts	%rax, %rdx		/* Create the encryption mask */
	mov	%rdx, %rax		/* ... and return it */

.Lno_sev_mask:
	movq	%rbp, %rsp		/* Restore original stack pointer */

	pop	%rdx
	pop	%rbp
#endif

	ret
ENDPROC(get_sev_encryption_mask)

	.data
enc_bit:
	.int	0xffffffff