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![Vaibhav Jain](/assets/img/avatar_default.png)
Presently when a user-space process issues CXL_IOCTL_START_WORK ioctl we store the pid of the current task_struct and use it to get pointer to the mm_struct of the process, while processing page or segment faults from the capi card. However this causes issues when the thread that had originally issued the start-work ioctl exits in which case the stored pid is no more valid and the cxl driver is unable to handle faults as the mm_struct corresponding to process is no more accessible. This patch fixes this issue by using the mm_struct of the next alive task in the thread group. This is done by iterating over all the tasks in the thread group starting from thread group leader and calling get_task_mm on each one of them. When a valid mm_struct is obtained the pid of the associated task is stored in the context replacing the exiting one for handling future faults. The patch introduces a new function named get_mem_context that checks if the current task pointed to by ctx->pid is dead? If yes it performs the steps described above. Also a new variable cxl_context.glpid is introduced which stores the pid of the thread group leader associated with the context owning task. Reported-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com> Reported-by: Frank Haverkamp <HAVERKAM@de.ibm.com> Suggested-by: Ian Munsie <imunsie@au1.ibm.com> Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com> Acked-by: Ian Munsie <imunsie@au1.ibm.com> Reviewed-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com> Reviewed-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
375 lines
9 KiB
C
375 lines
9 KiB
C
/*
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* Copyright 2014 IBM Corp.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/workqueue.h>
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#include <linux/sched.h>
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#include <linux/pid.h>
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#include <linux/mm.h>
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#include <linux/moduleparam.h>
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#undef MODULE_PARAM_PREFIX
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#define MODULE_PARAM_PREFIX "cxl" "."
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#include <asm/current.h>
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#include <asm/copro.h>
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#include <asm/mmu.h>
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#include "cxl.h"
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#include "trace.h"
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static bool sste_matches(struct cxl_sste *sste, struct copro_slb *slb)
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{
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return ((sste->vsid_data == cpu_to_be64(slb->vsid)) &&
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(sste->esid_data == cpu_to_be64(slb->esid)));
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}
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/*
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* This finds a free SSTE for the given SLB, or returns NULL if it's already in
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* the segment table.
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*/
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static struct cxl_sste* find_free_sste(struct cxl_context *ctx,
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struct copro_slb *slb)
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{
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struct cxl_sste *primary, *sste, *ret = NULL;
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unsigned int mask = (ctx->sst_size >> 7) - 1; /* SSTP0[SegTableSize] */
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unsigned int entry;
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unsigned int hash;
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if (slb->vsid & SLB_VSID_B_1T)
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hash = (slb->esid >> SID_SHIFT_1T) & mask;
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else /* 256M */
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hash = (slb->esid >> SID_SHIFT) & mask;
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primary = ctx->sstp + (hash << 3);
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for (entry = 0, sste = primary; entry < 8; entry++, sste++) {
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if (!ret && !(be64_to_cpu(sste->esid_data) & SLB_ESID_V))
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ret = sste;
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if (sste_matches(sste, slb))
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return NULL;
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}
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if (ret)
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return ret;
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/* Nothing free, select an entry to cast out */
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ret = primary + ctx->sst_lru;
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ctx->sst_lru = (ctx->sst_lru + 1) & 0x7;
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return ret;
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}
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static void cxl_load_segment(struct cxl_context *ctx, struct copro_slb *slb)
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{
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/* mask is the group index, we search primary and secondary here. */
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struct cxl_sste *sste;
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unsigned long flags;
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spin_lock_irqsave(&ctx->sste_lock, flags);
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sste = find_free_sste(ctx, slb);
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if (!sste)
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goto out_unlock;
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pr_devel("CXL Populating SST[%li]: %#llx %#llx\n",
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sste - ctx->sstp, slb->vsid, slb->esid);
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trace_cxl_ste_write(ctx, sste - ctx->sstp, slb->esid, slb->vsid);
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sste->vsid_data = cpu_to_be64(slb->vsid);
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sste->esid_data = cpu_to_be64(slb->esid);
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out_unlock:
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spin_unlock_irqrestore(&ctx->sste_lock, flags);
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}
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static int cxl_fault_segment(struct cxl_context *ctx, struct mm_struct *mm,
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u64 ea)
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{
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struct copro_slb slb = {0,0};
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int rc;
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if (!(rc = copro_calculate_slb(mm, ea, &slb))) {
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cxl_load_segment(ctx, &slb);
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}
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return rc;
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}
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static void cxl_ack_ae(struct cxl_context *ctx)
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{
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unsigned long flags;
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cxl_ack_irq(ctx, CXL_PSL_TFC_An_AE, 0);
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spin_lock_irqsave(&ctx->lock, flags);
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ctx->pending_fault = true;
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ctx->fault_addr = ctx->dar;
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ctx->fault_dsisr = ctx->dsisr;
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spin_unlock_irqrestore(&ctx->lock, flags);
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wake_up_all(&ctx->wq);
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}
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static int cxl_handle_segment_miss(struct cxl_context *ctx,
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struct mm_struct *mm, u64 ea)
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{
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int rc;
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pr_devel("CXL interrupt: Segment fault pe: %i ea: %#llx\n", ctx->pe, ea);
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trace_cxl_ste_miss(ctx, ea);
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if ((rc = cxl_fault_segment(ctx, mm, ea)))
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cxl_ack_ae(ctx);
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else {
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mb(); /* Order seg table write to TFC MMIO write */
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cxl_ack_irq(ctx, CXL_PSL_TFC_An_R, 0);
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}
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return IRQ_HANDLED;
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}
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static void cxl_handle_page_fault(struct cxl_context *ctx,
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struct mm_struct *mm, u64 dsisr, u64 dar)
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{
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unsigned flt = 0;
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int result;
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unsigned long access, flags, inv_flags = 0;
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trace_cxl_pte_miss(ctx, dsisr, dar);
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if ((result = copro_handle_mm_fault(mm, dar, dsisr, &flt))) {
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pr_devel("copro_handle_mm_fault failed: %#x\n", result);
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return cxl_ack_ae(ctx);
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}
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/*
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* update_mmu_cache() will not have loaded the hash since current->trap
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* is not a 0x400 or 0x300, so just call hash_page_mm() here.
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*/
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access = _PAGE_PRESENT;
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if (dsisr & CXL_PSL_DSISR_An_S)
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access |= _PAGE_RW;
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if ((!ctx->kernel) || ~(dar & (1ULL << 63)))
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access |= _PAGE_USER;
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if (dsisr & DSISR_NOHPTE)
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inv_flags |= HPTE_NOHPTE_UPDATE;
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local_irq_save(flags);
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hash_page_mm(mm, dar, access, 0x300, inv_flags);
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local_irq_restore(flags);
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pr_devel("Page fault successfully handled for pe: %i!\n", ctx->pe);
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cxl_ack_irq(ctx, CXL_PSL_TFC_An_R, 0);
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}
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/*
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* Returns the mm_struct corresponding to the context ctx via ctx->pid
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* In case the task has exited we use the task group leader accessible
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* via ctx->glpid to find the next task in the thread group that has a
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* valid mm_struct associated with it. If a task with valid mm_struct
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* is found the ctx->pid is updated to use the task struct for subsequent
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* translations. In case no valid mm_struct is found in the task group to
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* service the fault a NULL is returned.
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*/
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static struct mm_struct *get_mem_context(struct cxl_context *ctx)
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{
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struct task_struct *task = NULL;
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struct mm_struct *mm = NULL;
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struct pid *old_pid = ctx->pid;
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if (old_pid == NULL) {
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pr_warn("%s: Invalid context for pe=%d\n",
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__func__, ctx->pe);
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return NULL;
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}
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task = get_pid_task(old_pid, PIDTYPE_PID);
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/*
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* pid_alive may look racy but this saves us from costly
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* get_task_mm when the task is a zombie. In worst case
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* we may think a task is alive, which is about to die
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* but get_task_mm will return NULL.
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*/
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if (task != NULL && pid_alive(task))
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mm = get_task_mm(task);
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/* release the task struct that was taken earlier */
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if (task)
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put_task_struct(task);
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else
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pr_devel("%s: Context owning pid=%i for pe=%i dead\n",
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__func__, pid_nr(old_pid), ctx->pe);
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/*
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* If we couldn't find the mm context then use the group
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* leader to iterate over the task group and find a task
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* that gives us mm_struct.
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*/
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if (unlikely(mm == NULL && ctx->glpid != NULL)) {
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rcu_read_lock();
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task = pid_task(ctx->glpid, PIDTYPE_PID);
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if (task)
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do {
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mm = get_task_mm(task);
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if (mm) {
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ctx->pid = get_task_pid(task,
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PIDTYPE_PID);
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break;
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}
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task = next_thread(task);
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} while (task && !thread_group_leader(task));
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rcu_read_unlock();
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/* check if we switched pid */
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if (ctx->pid != old_pid) {
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if (mm)
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pr_devel("%s:pe=%i switch pid %i->%i\n",
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__func__, ctx->pe, pid_nr(old_pid),
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pid_nr(ctx->pid));
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else
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pr_devel("%s:Cannot find mm for pid=%i\n",
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__func__, pid_nr(old_pid));
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/* drop the reference to older pid */
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put_pid(old_pid);
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}
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}
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return mm;
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}
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void cxl_handle_fault(struct work_struct *fault_work)
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{
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struct cxl_context *ctx =
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container_of(fault_work, struct cxl_context, fault_work);
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u64 dsisr = ctx->dsisr;
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u64 dar = ctx->dar;
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struct mm_struct *mm = NULL;
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if (cxl_p2n_read(ctx->afu, CXL_PSL_DSISR_An) != dsisr ||
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cxl_p2n_read(ctx->afu, CXL_PSL_DAR_An) != dar ||
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cxl_p2n_read(ctx->afu, CXL_PSL_PEHandle_An) != ctx->pe) {
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/* Most likely explanation is harmless - a dedicated process
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* has detached and these were cleared by the PSL purge, but
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* warn about it just in case */
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dev_notice(&ctx->afu->dev, "cxl_handle_fault: Translation fault regs changed\n");
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return;
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}
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/* Early return if the context is being / has been detached */
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if (ctx->status == CLOSED) {
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cxl_ack_ae(ctx);
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return;
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}
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pr_devel("CXL BOTTOM HALF handling fault for afu pe: %i. "
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"DSISR: %#llx DAR: %#llx\n", ctx->pe, dsisr, dar);
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if (!ctx->kernel) {
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mm = get_mem_context(ctx);
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/* indicates all the thread in task group have exited */
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if (mm == NULL) {
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pr_devel("%s: unable to get mm for pe=%d pid=%i\n",
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__func__, ctx->pe, pid_nr(ctx->pid));
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cxl_ack_ae(ctx);
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return;
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} else {
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pr_devel("Handling page fault for pe=%d pid=%i\n",
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ctx->pe, pid_nr(ctx->pid));
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}
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}
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if (dsisr & CXL_PSL_DSISR_An_DS)
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cxl_handle_segment_miss(ctx, mm, dar);
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else if (dsisr & CXL_PSL_DSISR_An_DM)
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cxl_handle_page_fault(ctx, mm, dsisr, dar);
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else
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WARN(1, "cxl_handle_fault has nothing to handle\n");
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if (mm)
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mmput(mm);
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}
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static void cxl_prefault_one(struct cxl_context *ctx, u64 ea)
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{
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struct mm_struct *mm;
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mm = get_mem_context(ctx);
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if (mm == NULL) {
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pr_devel("cxl_prefault_one unable to get mm %i\n",
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pid_nr(ctx->pid));
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return;
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}
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cxl_fault_segment(ctx, mm, ea);
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mmput(mm);
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}
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static u64 next_segment(u64 ea, u64 vsid)
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{
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if (vsid & SLB_VSID_B_1T)
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ea |= (1ULL << 40) - 1;
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else
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ea |= (1ULL << 28) - 1;
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return ea + 1;
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}
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static void cxl_prefault_vma(struct cxl_context *ctx)
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{
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u64 ea, last_esid = 0;
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struct copro_slb slb;
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struct vm_area_struct *vma;
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int rc;
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struct mm_struct *mm;
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mm = get_mem_context(ctx);
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if (mm == NULL) {
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pr_devel("cxl_prefault_vm unable to get mm %i\n",
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pid_nr(ctx->pid));
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return;
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}
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down_read(&mm->mmap_sem);
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for (vma = mm->mmap; vma; vma = vma->vm_next) {
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for (ea = vma->vm_start; ea < vma->vm_end;
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ea = next_segment(ea, slb.vsid)) {
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rc = copro_calculate_slb(mm, ea, &slb);
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if (rc)
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continue;
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if (last_esid == slb.esid)
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continue;
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cxl_load_segment(ctx, &slb);
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last_esid = slb.esid;
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}
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}
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up_read(&mm->mmap_sem);
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mmput(mm);
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}
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void cxl_prefault(struct cxl_context *ctx, u64 wed)
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{
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switch (ctx->afu->prefault_mode) {
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case CXL_PREFAULT_WED:
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cxl_prefault_one(ctx, wed);
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break;
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case CXL_PREFAULT_ALL:
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cxl_prefault_vma(ctx);
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break;
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default:
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break;
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}
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}
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