mshv_vtl_asm.S

  1/* SPDX-License-Identifier: GPL-2.0
  2 *
  3 * Assembly level code for mshv_vtl VTL transition
  4 *
  5 * Copyright (c) 2025, Microsoft Corporation.
  6 *
  7 * Author:
  8 *   Naman Jain <namjain@microsoft.com>
  9 */
 10
 11#include <linux/linkage.h>
 12#include <linux/static_call_types.h>
 13#include <asm/asm.h>
 14#include <asm/asm-offsets.h>
 15#include <asm/frame.h>
 16#include "mshv-asm-offsets.h"
 17
 18	.text
 19	.section .noinstr.text, "ax"
 20/*
 21 * void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0)
 22 *
 23 * This function is used to context switch between different Virtual Trust Levels.
 24 * It is marked as 'noinstr' to prevent against instrumentation and debugging facilities.
 25 * NMIs aren't a problem because the NMI handler saves/restores CR2 specifically to guard
 26 * against #PFs in NMI context clobbering the guest state.
 27 */
 28SYM_FUNC_START(__mshv_vtl_return_call)
 29	/* Push callee save registers */
 30	pushq %rbp
 31	mov %rsp, %rbp
 32	pushq %r12
 33	pushq %r13
 34	pushq %r14
 35	pushq %r15
 36	pushq %rbx
 37
 38	/* register switch to VTL0 clobbers all registers except rax/rcx */
 39	mov %_ASM_ARG1, %rax
 40
 41	/* grab rbx/rbp/rsi/rdi/r8-r15 */
 42	mov MSHV_VTL_CPU_CONTEXT_rbx(%rax), %rbx
 43	mov MSHV_VTL_CPU_CONTEXT_rbp(%rax), %rbp
 44	mov MSHV_VTL_CPU_CONTEXT_rsi(%rax), %rsi
 45	mov MSHV_VTL_CPU_CONTEXT_rdi(%rax), %rdi
 46	mov MSHV_VTL_CPU_CONTEXT_r8(%rax), %r8
 47	mov MSHV_VTL_CPU_CONTEXT_r9(%rax), %r9
 48	mov MSHV_VTL_CPU_CONTEXT_r10(%rax), %r10
 49	mov MSHV_VTL_CPU_CONTEXT_r11(%rax), %r11
 50	mov MSHV_VTL_CPU_CONTEXT_r12(%rax), %r12
 51	mov MSHV_VTL_CPU_CONTEXT_r13(%rax), %r13
 52	mov MSHV_VTL_CPU_CONTEXT_r14(%rax), %r14
 53	mov MSHV_VTL_CPU_CONTEXT_r15(%rax), %r15
 54
 55	mov MSHV_VTL_CPU_CONTEXT_cr2(%rax), %rdx
 56	mov %rdx, %cr2
 57	mov MSHV_VTL_CPU_CONTEXT_rdx(%rax), %rdx
 58
 59	/* stash host registers on stack */
 60	pushq %rax
 61	pushq %rcx
 62
 63	xor %ecx, %ecx
 64
 65	/* make a hypercall to switch VTL */
 66	call STATIC_CALL_TRAMP_STR(__mshv_vtl_return_hypercall)
 67
 68	/* stash guest registers on stack, restore saved host copies */
 69	pushq %rax
 70	pushq %rcx
 71	mov 16(%rsp), %rcx
 72	mov 24(%rsp), %rax
 73
 74	mov %rdx, MSHV_VTL_CPU_CONTEXT_rdx(%rax)
 75	mov %cr2, %rdx
 76	mov %rdx, MSHV_VTL_CPU_CONTEXT_cr2(%rax)
 77	pop MSHV_VTL_CPU_CONTEXT_rcx(%rax)
 78	pop MSHV_VTL_CPU_CONTEXT_rax(%rax)
 79	add $16, %rsp
 80
 81	/* save rbx/rbp/rsi/rdi/r8-r15 */
 82	mov %rbx, MSHV_VTL_CPU_CONTEXT_rbx(%rax)
 83	mov %rbp, MSHV_VTL_CPU_CONTEXT_rbp(%rax)
 84	mov %rsi, MSHV_VTL_CPU_CONTEXT_rsi(%rax)
 85	mov %rdi, MSHV_VTL_CPU_CONTEXT_rdi(%rax)
 86	mov %r8,  MSHV_VTL_CPU_CONTEXT_r8(%rax)
 87	mov %r9,  MSHV_VTL_CPU_CONTEXT_r9(%rax)
 88	mov %r10, MSHV_VTL_CPU_CONTEXT_r10(%rax)
 89	mov %r11, MSHV_VTL_CPU_CONTEXT_r11(%rax)
 90	mov %r12, MSHV_VTL_CPU_CONTEXT_r12(%rax)
 91	mov %r13, MSHV_VTL_CPU_CONTEXT_r13(%rax)
 92	mov %r14, MSHV_VTL_CPU_CONTEXT_r14(%rax)
 93	mov %r15, MSHV_VTL_CPU_CONTEXT_r15(%rax)
 94
 95	/* pop callee-save registers r12-r15, rbx */
 96	pop %rbx
 97	pop %r15
 98	pop %r14
 99	pop %r13
100	pop %r12
101
102	pop %rbp
103	RET
104SYM_FUNC_END(__mshv_vtl_return_call)
105/*
106 * Make sure that static_call_key symbol: __SCK____mshv_vtl_return_hypercall is accessible here.
107 * Below code is inspired from __ADDRESSABLE(sym) macro. Symbol name is kept simple, to avoid
108 * naming it something like "__UNIQUE_ID_addressable___SCK____mshv_vtl_return_hypercall_662.0"
109 * which would otherwise have been generated by the macro.
110 */
111	.section	.discard.addressable,"aw"
112	.align 8
113	.type	mshv_vtl_return_sym, @object
114	.size	mshv_vtl_return_sym, 8
115mshv_vtl_return_sym:
116	.quad	__SCK____mshv_vtl_return_hypercall