256ca55476
The ARM64 port is currently using SP_EL0 for everything: kernel threads, user threads and exceptions. In addition when taking an exception the exception code is still using the thread SP without relying on any interrupt stack. If from one hand this makes the context switch really quick because the thread context is already on the thread stack so we have only to save one register (SP) for the whole context, on the other hand the major limitation introduced by this choice is that if for some reason the thread SP is corrupted or pointing to some unaccessible location (for example in case of stack overflow), the exception code is unable to recover or even deal with it. The usual way of dealing with this kind of problems is to use a dedicated interrupt stack on SP_EL1 when servicing the exceptions. The real drawback of this is that, in case of context switch, all the context must be copied from the shared interrupt stack into a thread-specific stack or structure, so it is really slow. We use here an hybrid approach, sacrificing a bit of stack space for a quicker context switch. While nothing really changes for kernel threads, for user threads we now use the privileged stack (already present to service syscalls) as interrupt stack. When an exception arrives the code now switches to use SP_EL1 that for user threads is always pointing inside the privileged portion of the stack of the current running thread. This achieves two things: (1) isolate exceptions and syscall code to use a stack that is isolated, privileged and not accessible to user threads and (2) the thread SP is not touched at all during exceptions, so it can be invalid or corrupted without any direct consequence. Signed-off-by: Carlo Caione <ccaione@baylibre.com>
55 lines
956 B
C
55 lines
956 B
C
/*
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* Copyright (c) 2019 Carlo Caione <ccaione@baylibre.com>
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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/**
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* @file
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* @brief Per-arch thread definition
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*
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* This file contains definitions for
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*
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* struct _thread_arch
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* struct _callee_saved
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*
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* necessary to instantiate instances of struct k_thread.
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*/
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#ifndef ZEPHYR_INCLUDE_ARCH_ARM64_THREAD_H_
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#define ZEPHYR_INCLUDE_ARCH_ARM64_THREAD_H_
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#ifndef _ASMLANGUAGE
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#include <zephyr/types.h>
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struct _callee_saved {
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uint64_t x19;
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uint64_t x20;
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uint64_t x21;
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uint64_t x22;
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uint64_t x23;
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uint64_t x24;
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uint64_t x25;
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uint64_t x26;
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uint64_t x27;
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uint64_t x28;
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uint64_t x29;
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uint64_t sp_el0;
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uint64_t sp_elx;
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uint64_t xzr;
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};
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typedef struct _callee_saved _callee_saved_t;
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struct _thread_arch {
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#ifdef CONFIG_USERSPACE
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struct arm_mmu_ptables *ptables;
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#endif
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};
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typedef struct _thread_arch _thread_arch_t;
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#endif /* _ASMLANGUAGE */
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#endif /* ZEPHYR_INCLUDE_ARCH_ARM64_THREAD_H_ */
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