On 28/06/2018 13:10, Mahesh J Salgaonkar wrote:
> From: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx>
>
> rtas_log_buf is a buffer to hold RTAS event data that are communicated
> to kernel by hypervisor. This buffer is then used to pass RTAS event
> data to user through proc fs. This buffer is allocated from vmalloc
> (non-linear mapping) area.
>
> On Machine check interrupt, register r3 points to RTAS extended event
> log passed by hypervisor that contains the MCE event. The pseries
> machine check handler then logs this error into rtas_log_buf. The
> rtas_log_buf is a vmalloc-ed (non-linear) buffer we end up taking up a
> page fault (vector 0x300) while accessing it. Since machine check
> interrupt handler runs in NMI context we can not afford to take any
> page fault. Page faults are not honored in NMI context and causes
> kernel panic. Apart from that, as Nick pointed out, pSeries_log_error()
> also takes a spin_lock while logging error which is not safe in NMI
> context. It may endup in deadlock if we get another MCE before releasing
> the lock. Fix this by deferring the logging of rtas error to irq work queue.
>
> Current implementation uses two different buffers to hold rtas error log
> depending on whether extended log is provided or not. This makes bit
> difficult to identify which buffer has valid data that needs to logged
> later in irq work. Simplify this using single buffer, one per paca, and
> copy rtas log to it irrespective of whether extended log is provided or
> not. Allocate this buffer below RMA region so that it can be accessed
> in real mode mce handler.
>
> Fixes: b96672dd840f ("powerpc: Machine check interrupt is a non-maskable interrupt")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/include/asm/paca.h | 3 ++
> arch/powerpc/platforms/pseries/ras.c | 39 +++++++++++++++++++++-----------
> arch/powerpc/platforms/pseries/setup.c | 16 +++++++++++++
> 3 files changed, 45 insertions(+), 13 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
> index 3f109a3e3edb..b441fef53077 100644
> --- a/arch/powerpc/include/asm/paca.h
> +++ b/arch/powerpc/include/asm/paca.h
> @@ -251,6 +251,9 @@ struct paca_struct {
> void *rfi_flush_fallback_area;
> u64 l1d_flush_size;
> #endif
> +#ifdef CONFIG_PPC_PSERIES
> + u8 *mce_data_buf; /* buffer to hold per cpu rtas errlog */
> +#endif /* CONFIG_PPC_PSERIES */
> } ____cacheline_aligned;
>
> extern void copy_mm_to_paca(struct mm_struct *mm);
> diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
> index 5e1ef9150182..f6ba9a2a4f84 100644
> --- a/arch/powerpc/platforms/pseries/ras.c
> +++ b/arch/powerpc/platforms/pseries/ras.c
> @@ -22,6 +22,7 @@
> #include <linux/of.h>
> #include <linux/fs.h>
> #include <linux/reboot.h>
> +#include <linux/irq_work.h>
>
> #include <asm/machdep.h>
> #include <asm/rtas.h>
> @@ -32,11 +33,13 @@
> static unsigned char ras_log_buf[RTAS_ERROR_LOG_MAX];
> static DEFINE_SPINLOCK(ras_log_buf_lock);
>
> -static char global_mce_data_buf[RTAS_ERROR_LOG_MAX];
> -static DEFINE_PER_CPU(__u64, mce_data_buf);
> -
> static int ras_check_exception_token;
>
> +static void mce_process_errlog_event(struct irq_work *work);
> +static struct irq_work mce_errlog_process_work = {
> + .func = mce_process_errlog_event,
> +};
> +
> #define EPOW_SENSOR_TOKEN 9
> #define EPOW_SENSOR_INDEX 0
>
> @@ -336,10 +339,9 @@ static irqreturn_t ras_error_interrupt(int irq, void *dev_id)
> * the actual r3 if possible, and a ptr to the error log entry
> * will be returned if found.
> *
> - * If the RTAS error is not of the extended type, then we put it in a per
> - * cpu 64bit buffer. If it is the extended type we use global_mce_data_buf.
> + * Use one buffer mce_data_buf per cpu to store RTAS error.
> *
> - * The global_mce_data_buf does not have any locks or protection around it,
> + * The mce_data_buf does not have any locks or protection around it,
> * if a second machine check comes in, or a system reset is done
> * before we have logged the error, then we will get corruption in the
> * error log. This is preferable over holding off on calling
> @@ -362,20 +364,19 @@ static struct rtas_error_log *fwnmi_get_errinfo(struct pt_regs *regs)
> savep = __va(regs->gpr[3]);
> regs->gpr[3] = savep[0]; /* restore original r3 */
>
> - /* If it isn't an extended log we can use the per cpu 64bit buffer */
> h = (struct rtas_error_log *)&savep[1];
> + /* Use the per cpu buffer from paca to store rtas error log */
> + memset(local_paca->mce_data_buf, 0, RTAS_ERROR_LOG_MAX);
> if (!rtas_error_extended(h)) {
> - memcpy(this_cpu_ptr(&mce_data_buf), h, sizeof(__u64));
> - errhdr = (struct rtas_error_log *)this_cpu_ptr(&mce_data_buf);
> + memcpy(local_paca->mce_data_buf, h, sizeof(__u64));
> } else {
> int len, error_log_length;
>
> error_log_length = 8 + rtas_error_extended_log_length(h);
> len = max_t(int, error_log_length, RTAS_ERROR_LOG_MAX);
> - memset(global_mce_data_buf, 0, RTAS_ERROR_LOG_MAX);
> - memcpy(global_mce_data_buf, h, len);
> - errhdr = (struct rtas_error_log *)global_mce_data_buf;
> + memcpy(local_paca->mce_data_buf, h, len);
> }
> + errhdr = (struct rtas_error_log *)local_paca->mce_data_buf;
You should drop errhdr in this function and simply do
return (struct rtas_error_log *)local_paca->mce_data_buf;
>
> return errhdr;
> }
> @@ -422,6 +423,17 @@ int pSeries_system_reset_exception(struct pt_regs *regs)
> return 0; /* need to perform reset */
> }
>
> +/*
> + * Process MCE rtas errlog event.
> + */
> +static void mce_process_errlog_event(struct irq_work *work)
> +{
> + struct rtas_error_log *err;
> +
> + err = fwnmi_get_errlog();
> + log_error((char *)err, ERR_TYPE_RTAS_LOG, 0);
> +}
> +
> /*
> * See if we can recover from a machine check exception.
> * This is only called on power4 (or above) and only via
> @@ -466,7 +478,8 @@ static int recover_mce(struct pt_regs *regs, struct rtas_error_log *err)
> recovered = 1;
> }
>
> - log_error((char *)err, ERR_TYPE_RTAS_LOG, 0);
> + /* Queue irq work to log this rtas event later. */
> + irq_work_queue(&mce_errlog_process_work);
>
> return recovered;
> }
> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
> index fdb32e056ef4..60a067a6e743 100644
> --- a/arch/powerpc/platforms/pseries/setup.c
> +++ b/arch/powerpc/platforms/pseries/setup.c
> @@ -41,6 +41,7 @@
> #include <linux/root_dev.h>
> #include <linux/of.h>
> #include <linux/of_pci.h>
> +#include <linux/memblock.h>
>
> #include <asm/mmu.h>
> #include <asm/processor.h>
> @@ -101,6 +102,9 @@ static void pSeries_show_cpuinfo(struct seq_file *m)
> static void __init fwnmi_init(void)
> {
> unsigned long system_reset_addr, machine_check_addr;
> + u8 *mce_data_buf;
> + unsigned int i;
> + int nr_cpus = num_possible_cpus();
>
> int ibm_nmi_register = rtas_token("ibm,nmi-register");
> if (ibm_nmi_register == RTAS_UNKNOWN_SERVICE)
> @@ -114,6 +118,18 @@ static void __init fwnmi_init(void)
> if (0 == rtas_call(ibm_nmi_register, 2, 1, NULL, system_reset_addr,
> machine_check_addr))
> fwnmi_active = 1;
> +
> + /*
> + * Allocate a chunk for per cpu buffer to hold rtas errorlog.
> + * It will be used in real mode mce handler, hence it needs to be
> + * below RMA.
> + */
> + mce_data_buf = __va(memblock_alloc_base(RTAS_ERROR_LOG_MAX * nr_cpus,
> + RTAS_ERROR_LOG_MAX, ppc64_rma_size));
> + for_each_possible_cpu(i) {
> + paca_ptrs[i]->mce_data_buf = mce_data_buf +
> + (RTAS_ERROR_LOG_MAX * i);
> + }
> }
>
> static void pseries_8259_cascade(struct irq_desc *desc)
>
