bl31/aarch64/ea_delegate.S

/*
 * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */


#include <asm_macros.S>
#include <assert_macros.S>
#include <context.h>
#include <ea_handle.h>


	.globl	handle_lower_el_ea_esb
	.globl	enter_lower_el_sync_ea
	.globl	enter_lower_el_async_ea


/*
 * Function to delegate External Aborts synchronized by ESB instruction at EL3
 * vector entry. This function assumes GP registers x0-x29 have been saved, and
 * are available for use. It delegates the handling of the EA to platform
 * handler, and returns only upon successfully handling the EA; otherwise
 * panics. On return from this function, the original exception handler is
 * expected to resume.
 */
func handle_lower_el_ea_esb
	mov	x0, #ERROR_EA_ESB
	mrs	x1, DISR_EL1
	b	ea_proceed
endfunc handle_lower_el_ea_esb


/*
 * This function forms the tail end of Synchronous Exception entry from lower
 * EL, and expects to handle only Synchronous External Aborts from lower EL. If
 * any other kind of exception is detected, then this function reports unhandled
 * exception.
 *
 * Since it's part of exception vector, this function doesn't expect any GP
 * registers to have been saved. It delegates the handling of the EA to platform
 * handler, and upon successfully handling the EA, exits EL3; otherwise panics.
 */
func enter_lower_el_sync_ea
	/*
	 * Explicitly save x30 so as to free up a register and to enable
	 * branching.
	 */
	str	x30, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_LR]

	mrs	x30, esr_el3
	ubfx	x30, x30, #ESR_EC_SHIFT, #ESR_EC_LENGTH

	/* Check for I/D aborts from lower EL */
	cmp	x30, #EC_IABORT_LOWER_EL
	b.eq	1f

	cmp	x30, #EC_DABORT_LOWER_EL
	b.ne	2f

1:
	/* Test for EA bit in the instruction syndrome */
	mrs	x30, esr_el3
	tbz	x30, #ESR_ISS_EABORT_EA_BIT, 2f

	/* Save GP registers */
	bl	save_gp_registers

	/* Setup exception class and syndrome arguments for platform handler */
	mov	x0, #ERROR_EA_SYNC
	mrs	x1, esr_el3
	adr	x30, el3_exit
	b	ea_proceed

2:
	/* Synchronous exceptions other than the above are assumed to be EA */
	ldr	x30, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_LR]
	no_ret	report_unhandled_exception
endfunc enter_lower_el_sync_ea


/*
 * This function handles SErrors from lower ELs.
 *
 * Since it's part of exception vector, this function doesn't expect any GP
 * registers to have been saved. It delegates the handling of the EA to platform
 * handler, and upon successfully handling the EA, exits EL3; otherwise panics.
 */
func enter_lower_el_async_ea
	/*
	 * Explicitly save x30 so as to free up a register and to enable
	 * branching
	 */
	str	x30, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_LR]

	/* Save GP registers */
	bl	save_gp_registers

	/* Setup exception class and syndrome arguments for platform handler */
	mov	x0, #ERROR_EA_ASYNC
	mrs	x1, esr_el3
	adr	x30, el3_exit
	b	ea_proceed
endfunc enter_lower_el_async_ea


/*
 * Delegate External Abort handling to platform's EA handler. This function
 * assumes that all GP registers have been saved by the caller.
 *
 * x0: EA reason
 * x1: EA syndrome
 */
func ea_proceed
	/* Save EL3 state */
	mrs	x2, spsr_el3
	mrs	x3, elr_el3
	stp	x2, x3, [sp, #CTX_EL3STATE_OFFSET + CTX_SPSR_EL3]

	/*
	 * Save ESR as handling might involve lower ELs, and returning back to
	 * EL3 from there would trample the original ESR.
	 */
	mrs	x4, scr_el3
	mrs	x5, esr_el3
	stp	x4, x5, [sp, #CTX_EL3STATE_OFFSET + CTX_SCR_EL3]

	/*
	 * Setup rest of arguments, and call platform External Abort handler.
	 *
	 * x0: EA reason (already in place)
	 * x1: Exception syndrome (already in place).
	 * x2: Cookie (unused for now).
	 * x3: Context pointer.
	 * x4: Flags (security state from SCR for now).
	 */
	mov	x2, xzr
	mov	x3, sp
	ubfx	x4, x4, #0, #1

	/* Switch to runtime stack */
	ldr	x5, [sp, #CTX_EL3STATE_OFFSET + CTX_RUNTIME_SP]
	msr	spsel, #0
	mov	sp, x5

	mov	x29, x30
#if ENABLE_ASSERTIONS
	/* Stash the stack pointer */
	mov	x28, sp
#endif
	bl	plat_ea_handler
	mov	x30, x29

#if ENABLE_ASSERTIONS
	/*
	 * Error handling flows might involve long jumps; so upon returning from
	 * the platform error handler, validate that the we've completely
	 * unwound the stack.
	 */
	mov	x27, sp
	cmp	x28, x27
	ASM_ASSERT(eq)
#endif

	/* Make SP point to context */
	msr	spsel, #1

	/* Restore EL3 state */
	ldp	x1, x2, [sp, #CTX_EL3STATE_OFFSET + CTX_SPSR_EL3]
	msr	spsr_el3, x1
	msr	elr_el3, x2

	/* Restore ESR_EL3 and SCR_EL3 */
	ldp	x3, x4, [sp, #CTX_EL3STATE_OFFSET + CTX_SCR_EL3]
	msr	scr_el3, x3
	msr	esr_el3, x4

	ret
endfunc ea_proceed