casaroli commented on code in PR #19797: URL: https://github.com/apache/nuttx/pull/19797#discussion_r4093748446
########## arch/xtensa/src/esp32s3/esp32s3_pagefault.c: ########## @@ -0,0 +1,135 @@ +/**************************************************************************** + * arch/xtensa/src/esp32s3/esp32s3_pagefault.c + * + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. The + * ASF licenses this file to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance with the + * License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT + * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the + * License for the specific language governing permissions and limitations + * under the License. + * + ****************************************************************************/ + +/**************************************************************************** + * Included Files + ****************************************************************************/ + +#include <nuttx/config.h> + +#include <stdbool.h> +#include <stdint.h> +#include <debug.h> +#include <errno.h> + +#include <nuttx/sched.h> +#include <arch/irq.h> +#include <arch/xtensa/xtensa_corebits.h> + +#include "xtensa.h" +#include "sched/sched.h" + +/**************************************************************************** + * Pre-processor Definitions + ****************************************************************************/ + +#ifdef CONFIG_ESP32S3_PAGEFAULT_SELFTEST +/* Runtime self-test: proof of the recoverable-fault primitive on silicon. + * A load of this out-of-cache-region address raises a precise LoadProhibited + * (EXCCAUSE 28, "cache attribute does not allow load") whose EXCVADDR tracks + * the address exactly. The dispatcher returns "serviced" WITHOUT making the + * address accessible for the first PF_SELFTEST_REPEATS re-executions, so the + * exception vector's RFE re-runs the identical faulting instruction. + * Being re-entered that many times for one instruction proves that RFE + * cleanly restarts a faulted precise access (the write-buffer / prefetch + * corner case that gates recoverable page faults); it then steps the saved + * PC past the 2-byte l32i.n so the faulting task resumes. Trigger it from a + * user task, e.g. examples/pffault: nsh> pffault r 0x80000000 + */ + +# define PF_SELFTEST_VADDR 0x80000000ul +# define PF_SELFTEST_REPEATS 3 + +/**************************************************************************** + * Private Data + ****************************************************************************/ + +static volatile int g_pf_selftest_hits; +#endif + +/**************************************************************************** + * Public Functions + ****************************************************************************/ + +/**************************************************************************** + * Name: esp32s3_pagefault_dispatch + * + * Description: + * Offered the precise, restartable exceptions raised by a cache-attribute + * permission violation (EXCCAUSE Load/Store/InstrFetch Prohibited). The + * faulting virtual address is in regs[REG_EXCVADDR] and the faulting PC in + * regs[REG_PC]; both are populated by the common Xtensa user exception + * handler (frame layout: NuttX REG_*). + * + * This unit establishes the recoverable-fault primitive. The full + * servicing (map a page / restore a cache attribute, then RFE-restart) is + * built on top in the addrenv / demand-paging units; here the dispatcher + * reports the fault (with its tracking EXCVADDR) and declines to service + * it, except under the self-test which proves the RFE-restart on silicon. + * + * Returned Value: + * OK if the faulting instruction may be (re-)executed via RFE; a negated + * errno otherwise (the caller then panics / aborts the faulting task). + * + ****************************************************************************/ + +int esp32s3_pagefault_dispatch(int exccause, uint32_t *regs) +{ + uintptr_t vaddr = (uintptr_t)regs[REG_EXCVADDR]; + uintptr_t pc = (uintptr_t)regs[REG_PC]; + +#ifdef CONFIG_ESP32S3_PAGEFAULT_SELFTEST + if (exccause == EXCCAUSE_LOAD_PROHIBITED && vaddr == PF_SELFTEST_VADDR) + { + g_pf_selftest_hits++; + + _alert("PAGEFAULT SELFTEST: restart #%d precise LoadProhibited " + "EXCVADDR=%08x PC=%08x\n", + g_pf_selftest_hits, (unsigned)vaddr, (unsigned)pc); + + if (g_pf_selftest_hits < PF_SELFTEST_REPEATS) + { + /* Return serviced without changing anything: the RFE must + * re-execute the identical faulting load and land back here. + */ + + return OK; + } + + /* Proof complete: step past the 2-byte l32i.n so the task resumes. */ + + regs[REG_PC] = pc + 2; + g_pf_selftest_hits = 0; + _alert("PAGEFAULT SELFTEST: RFE cleanly restarted the load %d times; " + "resuming\n", PF_SELFTEST_REPEATS); + return OK; + } +#endif + + /* Report the precise fault (with its tracking EXCVADDR) and decline to + * service it, so the caller falls through to the panic / abort path. + */ + + _alert("cache fault: EXCCAUSE=%d EXCVADDR=%08x PC=%08x task=%s\n", + exccause, (unsigned)vaddr, (unsigned)pc, Review Comment: done -- This is an automated message from the Apache Git Service. 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