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SubjectRe: [RFC PATCH v1 1/3] arm64/ras: support sea error recovery
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Hi Xie,

On 01/09/17 11:31, Xie XiuQi wrote:
> With ARM v8.2 RAS Extension, SEA are usually triggered when memory errors
> are consumed. In some cases, if the error address is in a clean page or a
> read-only page, there is a chance to recover. Such as error occurs in a
> instruction page, we can reread this page from disk instead of killing process.
>
> Because memory_failure() may sleep, we can not call it directly in SEA exception
> context. So we saved faulting physical address associated with a process in the
> ghes handler and set __TIF_SEA_NOTIFY. When we return from SEA exception context
> and get into do_notify_resume() before the process running, we could check it
> and call memory_failure() to do recovery. It's safe, because we are in process
> context.
>
> Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com>
> Signed-off-by: Wang Xiongfeng <wangxiongfeng2@huawei.com>
> ---
> arch/arm64/Kconfig | 11 +++
> arch/arm64/include/asm/ras.h | 27 +++++++
> arch/arm64/include/asm/thread_info.h | 4 +-
> arch/arm64/kernel/Makefile | 1 +
> arch/arm64/kernel/ras.c | 138 +++++++++++++++++++++++++++++++++++
> arch/arm64/kernel/signal.c | 8 ++
> arch/arm64/mm/fault.c | 27 +++++--
> drivers/acpi/apei/ghes.c | 2 +
> 8 files changed, 209 insertions(+), 9 deletions(-)
> create mode 100644 arch/arm64/include/asm/ras.h
> create mode 100644 arch/arm64/kernel/ras.c
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index dfd9086..7d44589 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -640,6 +640,17 @@ config HOTPLUG_CPU
> Say Y here to experiment with turning CPUs off and on. CPUs
> can be controlled through /sys/devices/system/cpu.
>
> +config ARM64_ERR_RECOV
> + bool "Support arm64 RAS error recovery"
> + depends on ACPI_APEI_SEA && MEMORY_FAILURE
> + help
> + With ARM v8.2 RAS Extension, SEA are usually triggered when memory errors
> + are consumed. In some cases, if the error address is in a clean page or a
> + read-only page, there is a chance to recover. Such as error occurs in a
> + instruction page, we can reread this page from disk instead of killing process.
> +
> + Say Y if unsure.
> +
> # Common NUMA Features
> config NUMA
> bool "Numa Memory Allocation and Scheduler Support"
> diff --git a/arch/arm64/include/asm/ras.h b/arch/arm64/include/asm/ras.h
> new file mode 100644
> index 0000000..8c4f6a8
> --- /dev/null
> +++ b/arch/arm64/include/asm/ras.h
> @@ -0,0 +1,27 @@
> +/*
> + * ARM64 SEA error recoery support
> + *
> + * Copyright 2017 Huawei Technologies Co., Ltd.
> + * Author: Xie XiuQi <xiexiuqi@huawei.com>
> + * Author: Wang Xiongfeng <wangxiongfeng2@huawei.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License version
> + * 2 as published by the Free Software Foundation;
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#ifndef _ASM_RAS_H
> +#define _ASM_RAS_H
> +
> +#include <linux/cper.h>
> +#include <acpi/ghes.h>
> +
> +extern void sea_notify_process(void);
> +extern void arm_proc_error_check(struct ghes *ghes, struct cper_sec_proc_arm *err);
> +
> +#endif /*_ASM_RAS_H*/
> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index 46c3b93..4b10131 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -86,6 +86,7 @@ struct thread_info {
> #define TIF_NOTIFY_RESUME 2 /* callback before returning to user */
> #define TIF_FOREIGN_FPSTATE 3 /* CPU's FP state is not current's */
> #define TIF_UPROBE 4 /* uprobe breakpoint or singlestep */
> +#define TIF_SEA_NOTIFY 5 /* notify to do an error recovery */
> #define TIF_NOHZ 7
> #define TIF_SYSCALL_TRACE 8
> #define TIF_SYSCALL_AUDIT 9
> @@ -102,6 +103,7 @@ struct thread_info {
> #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
> #define _TIF_FOREIGN_FPSTATE (1 << TIF_FOREIGN_FPSTATE)
> #define _TIF_NOHZ (1 << TIF_NOHZ)
> +#define _TIF_SEA_NOTIFY (1 << TIF_SEA_NOTIFY)
> #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
> #define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
> #define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
> @@ -111,7 +113,7 @@ struct thread_info {
>
> #define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
> _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
> - _TIF_UPROBE)
> + _TIF_UPROBE|_TIF_SEA_NOTIFY)
>
> #define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
> _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index f2b4e81..ba3abf8 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -43,6 +43,7 @@ arm64-obj-$(CONFIG_EFI) += efi.o efi-entry.stub.o
> arm64-obj-$(CONFIG_PCI) += pci.o
> arm64-obj-$(CONFIG_ARMV8_DEPRECATED) += armv8_deprecated.o
> arm64-obj-$(CONFIG_ACPI) += acpi.o
> +arm64-obj-$(CONFIG_ARM64_ERR_RECOV) += ras.o
> arm64-obj-$(CONFIG_ACPI_NUMA) += acpi_numa.o
> arm64-obj-$(CONFIG_ARM64_ACPI_PARKING_PROTOCOL) += acpi_parking_protocol.o
> arm64-obj-$(CONFIG_PARAVIRT) += paravirt.o
> diff --git a/arch/arm64/kernel/ras.c b/arch/arm64/kernel/ras.c
> new file mode 100644
> index 0000000..8562ec7
> --- /dev/null
> +++ b/arch/arm64/kernel/ras.c
> @@ -0,0 +1,138 @@
> +/*
> + * ARM64 SEA error recoery support
> + *
> + * Copyright 2017 Huawei Technologies Co., Ltd.
> + * Author: Xie XiuQi <xiexiuqi@huawei.com>
> + * Author: Wang Xiongfeng <wangxiongfeng2@huawei.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License version
> + * 2 as published by the Free Software Foundation;
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/cper.h>
> +#include <linux/mm.h>
> +#include <linux/preempt.h>
> +#include <linux/acpi.h>
> +#include <linux/sched/signal.h>
> +
> +#include <acpi/actbl1.h>
> +#include <acpi/ghes.h>
> +#include <acpi/apei.h>
> +
> +#include <asm/thread_info.h>
> +#include <asm/atomic.h>
> +#include <asm/ras.h>
> +
> +/*
> + * Need to save faulting physical address associated with a process
> + * in the sea ghes handler some place where we can grab it back
> + * later in sea_notify_process()
> + */
> +#define SEA_INFO_MAX 16
> +
> +struct sea_info {
> + atomic_t inuse;
> + struct task_struct *t;
> + __u64 paddr;
> +} sea_info[SEA_INFO_MAX];
> +
> +static int sea_save_info(__u64 addr)
> +{
> + struct sea_info *si;
> +
> + for (si = sea_info; si < &sea_info[SEA_INFO_MAX]; si++) {
> + if (atomic_cmpxchg(&si->inuse, 0, 1) == 0) {
> + si->t = current;
> + si->paddr = addr;
> + return 0;
> + }
> + }
> +
> + pr_err("Too many concurrent recoverable errors\n");
> + return -ENOMEM;
> +}
> +
> +static struct sea_info *sea_find_info(void)
> +{
> + struct sea_info *si;
> +
> + for (si = sea_info; si < &sea_info[SEA_INFO_MAX]; si++)
> + if (atomic_read(&si->inuse) && si->t == current)
> + return si;
> + return NULL;
> +}
> +
> +static void sea_clear_info(struct sea_info *si)
> +{
> + atomic_set(&si->inuse, 0);
> +}
> +
> +/*
> + * Called in process context that interrupted by SEA and marked with
> + * TIF_SEA_NOTIFY, just before returning to erroneous userland.
> + * This code is allowed to sleep.
> + * Attempt possible recovery such as calling the high level VM handler to
> + * process any corrupted pages, and kill/signal current process if required.
> + * Action required errors are handled here.
> + */
> +void sea_notify_process(void)
> +{
> + unsigned long pfn;
> + int fail = 0, flags = MF_ACTION_REQUIRED;
> + struct sea_info *si = sea_find_info();
> +
> + if (!si)
> + panic("Lost physical address for consumed uncorrectable error");
> +
> + clear_thread_flag(TIF_SEA_NOTIFY);
> + do {
> + pfn = si->paddr >> PAGE_SHIFT;
> +
> +
> + pr_err("Uncorrected hardware memory error in user-access at %llx\n",
> + si->paddr);
> + /*
> + * We must call memory_failure() here even if the current process is
> + * doomed. We still need to mark the page as poisoned and alert any
> + * other users of the page.
> + */
> + if (memory_failure(pfn, 0, flags) < 0) {
> + fail++;
> + }
> + sea_clear_info(si);
> +
> + si = sea_find_info();
> + } while (si);
> +
> + if (fail) {
> + pr_err("Memory error not recovered\n");
> + force_sig(SIGBUS, current);
> + }
> +}
> +
> +void arm_proc_error_check(struct ghes *ghes, struct cper_sec_proc_arm *err)
> +{
> + int i, ret = -1;
> + struct cper_arm_err_info *err_info;
> +
> + if ((ghes->generic->notify.type != ACPI_HEST_NOTIFY_SEA) ||
> + (ghes->estatus->error_severity != CPER_SEV_RECOVERABLE))
> + return;
> +
> + err_info = (struct cper_arm_err_info *)(err + 1);
> + for (i = 0; i < err->err_info_num; i++, err_info++) {
> + if (err_info->validation_bits & CPER_ARM_INFO_VALID_PHYSICAL_ADDR) {
> + ret |= sea_save_info(err_info->physical_fault_addr);
> + }
> + }
> +
> + if (!ret)

If ret is initialized to -1, this is never true since you only OR bits
in ret.

Should the body of the loop be:
ret &= sea_save_info(err_info->physical_fault_addr);

so as long as you as you manage to store 1 sea_info you set the thread flag?

But if that's the case a boolean might make more sense:

bool info_saved = false;
[...]
info_saved |= !sea_save_info(err_info->physical_fault_addr);
[...]
if (info_saved)
[...]


> + set_thread_flag(TIF_SEA_NOTIFY);
> +}
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index 089c3747..71e314e 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -38,6 +38,7 @@
> #include <asm/fpsimd.h>
> #include <asm/signal32.h>
> #include <asm/vdso.h>
> +#include <asm/ras.h>
>
> /*
> * Do a signal return; undo the signal stack. These are aligned to 128-bit.
> @@ -749,6 +750,13 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
> * Update the trace code with the current status.
> */
> trace_hardirqs_off();
> +
> +#ifdef CONFIG_ARM64_ERR_RECOV
> + /* notify userspace of pending SEAs */
> + if (thread_flags & _TIF_SEA_NOTIFY)
> + sea_notify_process();
> +#endif /* CONFIG_ARM64_ERR_RECOV */
> +
> do {
> if (thread_flags & _TIF_NEED_RESCHED) {
> schedule();
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 1f22a41..b38476d 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -594,14 +594,25 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
> nmi_exit();
> }
>
> - info.si_signo = SIGBUS;
> - info.si_errno = 0;
> - info.si_code = 0;
> - if (esr & ESR_ELx_FnV)
> - info.si_addr = NULL;
> - else
> - info.si_addr = (void __user *)addr;
> - arm64_notify_die("", regs, &info, esr);
> + if (user_mode(regs)) {
> + if (test_thread_flag(TIF_SEA_NOTIFY))
> + return ret;
> +
> + info.si_signo = SIGBUS;
> + info.si_errno = 0;
> + info.si_code = 0;
> + if (esr & ESR_ELx_FnV)
> + info.si_addr = NULL;
> + else
> + info.si_addr = (void __user *)addr;
> +
> + current->thread.fault_address = 0;
> + current->thread.fault_code = esr;
> + force_sig_info(info.si_signo, &info, current);
> + } else {
> + die("Uncorrected hardware memory error in kernel-access\n",
> + regs, esr);
> + }
>
> return ret;
> }
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index d661d45..fa9400d 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -52,6 +52,7 @@
> #include <acpi/ghes.h>
> #include <acpi/apei.h>
> #include <asm/tlbflush.h>
> +#include <asm/ras.h>
> #include <ras/ras_event.h>
>
> #include "apei-internal.h"
> @@ -520,6 +521,7 @@ static void ghes_do_proc(struct ghes *ghes,
> else if (guid_equal(sec_type, &CPER_SEC_PROC_ARM)) {
> struct cper_sec_proc_arm *err = acpi_hest_get_payload(gdata);
>
> + arm_proc_error_check(ghes, err);

If I understand the Makefile change correctly, arm_proc_error_check is
compiled only when CONFIG_ARM64_ERR_RECOV, don't you get a linker error
here if this config is not selected?

Otherwise patch looks fine.

Cheers,

--
Julien Thierry
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