arch/arm64/kvm/hyp/entry.S

/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Copyright (C) 2015 - ARM Ltd
 * Author: Marc Zyngier <marc.zyngier@arm.com>
 */

#include <linux/linkage.h>

#include <asm/alternative.h>
#include <asm/asm-offsets.h>
#include <asm/assembler.h>
#include <asm/fpsimdmacros.h>
#include <asm/kvm.h>
#include <asm/kvm_arm.h>
#include <asm/kvm_asm.h>
#include <asm/kvm_mmu.h>
#include <asm/kvm_ptrauth.h>

#define CPU_XREG_OFFSET(x)	(CPU_USER_PT_REGS + 8*x)
#define CPU_SP_EL0_OFFSET	(CPU_XREG_OFFSET(30) + 8)

	.text

/*
 * We treat x18 as callee-saved as the host may use it as a platform
 * register (e.g. for shadow call stack).
 */
.macro save_callee_saved_regs ctxt
	str	x18,      [\ctxt, #CPU_XREG_OFFSET(18)]
	stp	x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)]
	stp	x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)]
	stp	x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)]
	stp	x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)]
	stp	x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)]
	stp	x29, lr,  [\ctxt, #CPU_XREG_OFFSET(29)]
.endm

.macro restore_callee_saved_regs ctxt
	// We require \ctxt is not x18-x28
	ldr	x18,      [\ctxt, #CPU_XREG_OFFSET(18)]
	ldp	x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)]
	ldp	x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)]
	ldp	x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)]
	ldp	x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)]
	ldp	x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)]
	ldp	x29, lr,  [\ctxt, #CPU_XREG_OFFSET(29)]
.endm

.macro save_sp_el0 ctxt, tmp
	mrs	\tmp,	sp_el0
	str	\tmp,	[\ctxt, #CPU_SP_EL0_OFFSET]
.endm

.macro restore_sp_el0 ctxt, tmp
	ldr	\tmp,	  [\ctxt, #CPU_SP_EL0_OFFSET]
	msr	sp_el0, \tmp
.endm

/*
 * u64 __guest_enter(struct kvm_vcpu *vcpu,
 *		     struct kvm_cpu_context *host_ctxt);
 */
SYM_FUNC_START(__guest_enter)
	// x0: vcpu
	// x1: host context
	// x2-x17: clobbered by macros
	// x29: guest context

	// Store the host regs
	save_callee_saved_regs x1

	// Save the host's sp_el0
	save_sp_el0	x1, x2

	// Now the host state is stored if we have a pending RAS SError it must
	// affect the host. If any asynchronous exception is pending we defer
	// the guest entry. The DSB isn't necessary before v8.2 as any SError
	// would be fatal.
alternative_if ARM64_HAS_RAS_EXTN
	dsb	nshst
	isb
alternative_else_nop_endif
	mrs	x1, isr_el1
	cbz	x1,  1f
	mov	x0, #ARM_EXCEPTION_IRQ
	ret

1:
	add	x29, x0, #VCPU_CONTEXT

	// Macro ptrauth_switch_to_guest format:
	// 	ptrauth_switch_to_guest(guest cxt, tmp1, tmp2, tmp3)
	// The below macro to restore guest keys is not implemented in C code
	// as it may cause Pointer Authentication key signing mismatch errors
	// when this feature is enabled for kernel code.
	ptrauth_switch_to_guest x29, x0, x1, x2

	// Restore the guest's sp_el0
	restore_sp_el0 x29, x0

	// Restore guest regs x0-x17
	ldp	x0, x1,   [x29, #CPU_XREG_OFFSET(0)]
	ldp	x2, x3,   [x29, #CPU_XREG_OFFSET(2)]
	ldp	x4, x5,   [x29, #CPU_XREG_OFFSET(4)]
	ldp	x6, x7,   [x29, #CPU_XREG_OFFSET(6)]
	ldp	x8, x9,   [x29, #CPU_XREG_OFFSET(8)]
	ldp	x10, x11, [x29, #CPU_XREG_OFFSET(10)]
	ldp	x12, x13, [x29, #CPU_XREG_OFFSET(12)]
	ldp	x14, x15, [x29, #CPU_XREG_OFFSET(14)]
	ldp	x16, x17, [x29, #CPU_XREG_OFFSET(16)]

	// Restore guest regs x18-x29, lr
	restore_callee_saved_regs x29

	// Do not touch any register after this!
	eret
	sb

SYM_INNER_LABEL(__guest_exit, SYM_L_GLOBAL)
	// x0: return code
	// x1: vcpu
	// x2-x29,lr: vcpu regs
	// vcpu x0-x1 on the stack

	add	x1, x1, #VCPU_CONTEXT

	ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN)

	// Store the guest regs x2 and x3
	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]

	// Retrieve the guest regs x0-x1 from the stack
	ldp	x2, x3, [sp], #16	// x0, x1

	// Store the guest regs x0-x1 and x4-x17
	stp	x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
	stp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
	stp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
	stp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
	stp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
	stp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
	stp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
	stp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]

	// Store the guest regs x18-x29, lr
	save_callee_saved_regs x1

	// Store the guest's sp_el0
	save_sp_el0	x1, x2

	get_host_ctxt	x2, x3

	// Macro ptrauth_switch_to_guest format:
	// 	ptrauth_switch_to_host(guest cxt, host cxt, tmp1, tmp2, tmp3)
	// The below macro to save/restore keys is not implemented in C code
	// as it may cause Pointer Authentication key signing mismatch errors
	// when this feature is enabled for kernel code.
	ptrauth_switch_to_host x1, x2, x3, x4, x5

	// Restore the hosts's sp_el0
	restore_sp_el0 x2, x3

	// Now restore the host regs
	restore_callee_saved_regs x2

alternative_if ARM64_HAS_RAS_EXTN
	// If we have the RAS extensions we can consume a pending error
	// without an unmask-SError and isb. The ESB-instruction consumed any
	// pending guest error when we took the exception from the guest.
	mrs_s	x2, SYS_DISR_EL1
	str	x2, [x1, #(VCPU_FAULT_DISR - VCPU_CONTEXT)]
	cbz	x2, 1f
	msr_s	SYS_DISR_EL1, xzr
	orr	x0, x0, #(1<<ARM_EXIT_WITH_SERROR_BIT)
1:	ret
alternative_else
	dsb	sy		// Synchronize against in-flight ld/st
	isb			// Prevent an early read of side-effect free ISR
	mrs	x2, isr_el1
	tbnz	x2, #8, 2f	// ISR_EL1.A
	ret
	nop
2:
alternative_endif
	// We know we have a pending asynchronous abort, now is the
	// time to flush it out. From your VAXorcist book, page 666:
	// "Threaten me not, oh Evil one!  For I speak with
	// the power of DEC, and I command thee to show thyself!"
	mrs	x2, elr_el2
	mrs	x3, esr_el2
	mrs	x4, spsr_el2
	mov	x5, x0

	msr	daifclr, #4	// Unmask aborts

	// This is our single instruction exception window. A pending
	// SError is guaranteed to occur at the earliest when we unmask
	// it, and at the latest just after the ISB.
	.global	abort_guest_exit_start
abort_guest_exit_start:

	isb

	.global	abort_guest_exit_end
abort_guest_exit_end:

	msr	daifset, #4	// Mask aborts

	// If the exception took place, restore the EL1 exception
	// context so that we can report some information.
	// Merge the exception code with the SError pending bit.
	tbz	x0, #ARM_EXIT_WITH_SERROR_BIT, 1f
	msr	elr_el2, x2
	msr	esr_el2, x3
	msr	spsr_el2, x4
	orr	x0, x0, x5
1:	ret
SYM_FUNC_END(__guest_enter)