Excerpts from Haren Myneni's message of June 18, 2021 6:32 am:
>
> If a coprocessor encounters an error translating an address, the
> VAS will cause an interrupt in the host. The kernel processes
> the fault by updating CSB. This functionality is same for both
> powerNV and pseries. So this patch moves these functions to
> common vas-api.c and the actual functionality is not changed.
>
> Signed-off-by: Haren Myneni <ha...@linux.ibm.com>
> Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> ---
> arch/powerpc/include/asm/vas.h | 3 +
> arch/powerpc/platforms/book3s/vas-api.c | 167 +++++++++++++++++++++
> arch/powerpc/platforms/powernv/vas-fault.c | 155 ++-----------------
> 3 files changed, 179 insertions(+), 146 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/vas.h b/arch/powerpc/include/asm/vas.h
> index 71cff6d6bf3a..6b41c0818958 100644
> --- a/arch/powerpc/include/asm/vas.h
> +++ b/arch/powerpc/include/asm/vas.h
> @@ -230,4 +230,7 @@ int vas_register_coproc_api(struct module *mod, enum
> vas_cop_type cop_type,
> void vas_unregister_coproc_api(void);
>
> int get_vas_user_win_ref(struct vas_user_win_ref *task_ref);
> +void vas_update_csb(struct coprocessor_request_block *crb,
> + struct vas_user_win_ref *task_ref);
> +void vas_dump_crb(struct coprocessor_request_block *crb);
> #endif /* __ASM_POWERPC_VAS_H */
> diff --git a/arch/powerpc/platforms/book3s/vas-api.c
> b/arch/powerpc/platforms/book3s/vas-api.c
> index 4ce82500f4c5..30172e52e16b 100644
> --- a/arch/powerpc/platforms/book3s/vas-api.c
> +++ b/arch/powerpc/platforms/book3s/vas-api.c
> @@ -10,6 +10,9 @@
> #include <linux/fs.h>
> #include <linux/slab.h>
> #include <linux/uaccess.h>
> +#include <linux/kthread.h>
> +#include <linux/sched/signal.h>
> +#include <linux/mmu_context.h>
> #include <linux/io.h>
> #include <asm/vas.h>
> #include <uapi/asm/vas-api.h>
> @@ -94,6 +97,170 @@ int get_vas_user_win_ref(struct vas_user_win_ref
> *task_ref)
> return 0;
> }
>
> +/*
> + * Successful return must release the task reference with
> + * put_task_struct
> + */
> +static bool ref_get_pid_and_task(struct vas_user_win_ref *task_ref,
> + struct task_struct **tskp, struct pid **pidp)
> +{
> + struct task_struct *tsk;
> + struct pid *pid;
> +
> + pid = task_ref->pid;
> + tsk = get_pid_task(pid, PIDTYPE_PID);
> + if (!tsk) {
> + pid = task_ref->tgid;
> + tsk = get_pid_task(pid, PIDTYPE_PID);
> + /*
> + * Parent thread (tgid) will be closing window when it
> + * exits. So should not get here.
> + */
> + if (WARN_ON_ONCE(!tsk))
> + return false;
> + }
> +
> + /* Return if the task is exiting. */
> + if (tsk->flags & PF_EXITING) {
> + put_task_struct(tsk);
> + return false;
> + }
> +
> + *tskp = tsk;
> + *pidp = pid;
> +
> + return true;
> +}
Thanks for making this change.
I think that's good to factor all these out and put them together.
Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> +
> +/*
> + * Update the CSB to indicate a translation error.
> + *
> + * User space will be polling on CSB after the request is issued.
> + * If NX can handle the request without any issues, it updates CSB.
> + * Whereas if NX encounters page fault, the kernel will handle the
> + * fault and update CSB with translation error.
> + *
> + * If we are unable to update the CSB means copy_to_user failed due to
> + * invalid csb_addr, send a signal to the process.
> + */
> +void vas_update_csb(struct coprocessor_request_block *crb,
> + struct vas_user_win_ref *task_ref)
> +{
> + struct coprocessor_status_block csb;
> + struct kernel_siginfo info;
> + struct task_struct *tsk;
> + void __user *csb_addr;
> + struct pid *pid;
> + int rc;
> +
> + /*
> + * NX user space windows can not be opened for task->mm=NULL
> + * and faults will not be generated for kernel requests.
> + */
> + if (WARN_ON_ONCE(!task_ref->mm))
> + return;
> +
> + csb_addr = (void __user *)be64_to_cpu(crb->csb_addr);
> +
> + memset(&csb, 0, sizeof(csb));
> + csb.cc = CSB_CC_FAULT_ADDRESS;
> + csb.ce = CSB_CE_TERMINATION;
> + csb.cs = 0;
> + csb.count = 0;
> +
> + /*
> + * NX operates and returns in BE format as defined CRB struct.
> + * So saves fault_storage_addr in BE as NX pastes in FIFO and
> + * expects user space to convert to CPU format.
> + */
> + csb.address = crb->stamp.nx.fault_storage_addr;
> + csb.flags = 0;
> +
> + /*
> + * Process closes send window after all pending NX requests are
> + * completed. In multi-thread applications, a child thread can
> + * open a window and can exit without closing it. May be some
> + * requests are pending or this window can be used by other
> + * threads later. We should handle faults if NX encounters
> + * pages faults on these requests. Update CSB with translation
> + * error and fault address. If csb_addr passed by user space is
> + * invalid, send SEGV signal to pid saved in window. If the
> + * child thread is not running, send the signal to tgid.
> + * Parent thread (tgid) will close this window upon its exit.
> + *
> + * pid and mm references are taken when window is opened by
> + * process (pid). So tgid is used only when child thread opens
> + * a window and exits without closing it.
> + */
> +
> + if (!ref_get_pid_and_task(task_ref, &tsk, &pid))
> + return;
> +
> + kthread_use_mm(task_ref->mm);
> + rc = copy_to_user(csb_addr, &csb, sizeof(csb));
> + /*
> + * User space polls on csb.flags (first byte). So add barrier
> + * then copy first byte with csb flags update.
> + */
> + if (!rc) {
> + csb.flags = CSB_V;
> + /* Make sure update to csb.flags is visible now */
> + smp_mb();
> + rc = copy_to_user(csb_addr, &csb, sizeof(u8));
> + }
> + kthread_unuse_mm(task_ref->mm);
> + put_task_struct(tsk);
> +
> + /* Success */
> + if (!rc)
> + return;
> +
> +
> + pr_debug("Invalid CSB address 0x%p signalling pid(%d)\n",
> + csb_addr, pid_vnr(pid));
> +
> + clear_siginfo(&info);
> + info.si_signo = SIGSEGV;
> + info.si_errno = EFAULT;
> + info.si_code = SEGV_MAPERR;
> + info.si_addr = csb_addr;
> + /*
> + * process will be polling on csb.flags after request is sent to
> + * NX. So generally CSB update should not fail except when an
> + * application passes invalid csb_addr. So an error message will
> + * be displayed and leave it to user space whether to ignore or
> + * handle this signal.
> + */
> + rcu_read_lock();
> + rc = kill_pid_info(SIGSEGV, &info, pid);
> + rcu_read_unlock();
> +
> + pr_devel("%s(): pid %d kill_proc_info() rc %d\n", __func__,
> + pid_vnr(pid), rc);
> +}
> +
> +void vas_dump_crb(struct coprocessor_request_block *crb)
> +{
> + struct data_descriptor_entry *dde;
> + struct nx_fault_stamp *nx;
> +
> + dde = &crb->source;
> + pr_devel("SrcDDE: addr 0x%llx, len %d, count %d, idx %d, flags %d\n",
> + be64_to_cpu(dde->address), be32_to_cpu(dde->length),
> + dde->count, dde->index, dde->flags);
> +
> + dde = &crb->target;
> + pr_devel("TgtDDE: addr 0x%llx, len %d, count %d, idx %d, flags %d\n",
> + be64_to_cpu(dde->address), be32_to_cpu(dde->length),
> + dde->count, dde->index, dde->flags);
> +
> + nx = &crb->stamp.nx;
> + pr_devel("NX Stamp: PSWID 0x%x, FSA 0x%llx, flags 0x%x, FS 0x%x\n",
> + be32_to_cpu(nx->pswid),
> + be64_to_cpu(crb->stamp.nx.fault_storage_addr),
> + nx->flags, nx->fault_status);
> +}
> +
> static int coproc_open(struct inode *inode, struct file *fp)
> {
> struct coproc_instance *cp_inst;
> diff --git a/arch/powerpc/platforms/powernv/vas-fault.c
> b/arch/powerpc/platforms/powernv/vas-fault.c
> index ac3a71ec3bd5..2729ac541fb3 100644
> --- a/arch/powerpc/platforms/powernv/vas-fault.c
> +++ b/arch/powerpc/platforms/powernv/vas-fault.c
> @@ -26,150 +26,6 @@
> */
> #define VAS_FAULT_WIN_FIFO_SIZE (4 << 20)
>
> -static void dump_crb(struct coprocessor_request_block *crb)
> -{
> - struct data_descriptor_entry *dde;
> - struct nx_fault_stamp *nx;
> -
> - dde = &crb->source;
> - pr_devel("SrcDDE: addr 0x%llx, len %d, count %d, idx %d, flags %d\n",
> - be64_to_cpu(dde->address), be32_to_cpu(dde->length),
> - dde->count, dde->index, dde->flags);
> -
> - dde = &crb->target;
> - pr_devel("TgtDDE: addr 0x%llx, len %d, count %d, idx %d, flags %d\n",
> - be64_to_cpu(dde->address), be32_to_cpu(dde->length),
> - dde->count, dde->index, dde->flags);
> -
> - nx = &crb->stamp.nx;
> - pr_devel("NX Stamp: PSWID 0x%x, FSA 0x%llx, flags 0x%x, FS 0x%x\n",
> - be32_to_cpu(nx->pswid),
> - be64_to_cpu(crb->stamp.nx.fault_storage_addr),
> - nx->flags, nx->fault_status);
> -}
> -
> -/*
> - * Update the CSB to indicate a translation error.
> - *
> - * User space will be polling on CSB after the request is issued.
> - * If NX can handle the request without any issues, it updates CSB.
> - * Whereas if NX encounters page fault, the kernel will handle the
> - * fault and update CSB with translation error.
> - *
> - * If we are unable to update the CSB means copy_to_user failed due to
> - * invalid csb_addr, send a signal to the process.
> - */
> -static void update_csb(struct vas_window *window,
> - struct coprocessor_request_block *crb)
> -{
> - struct coprocessor_status_block csb;
> - struct kernel_siginfo info;
> - struct task_struct *tsk;
> - void __user *csb_addr;
> - struct pid *pid;
> - int rc;
> -
> - /*
> - * NX user space windows can not be opened for task->mm=NULL
> - * and faults will not be generated for kernel requests.
> - */
> - if (WARN_ON_ONCE(!window->task_ref.mm || !window->user_win))
> - return;
> -
> - csb_addr = (void __user *)be64_to_cpu(crb->csb_addr);
> -
> - memset(&csb, 0, sizeof(csb));
> - csb.cc = CSB_CC_FAULT_ADDRESS;
> - csb.ce = CSB_CE_TERMINATION;
> - csb.cs = 0;
> - csb.count = 0;
> -
> - /*
> - * NX operates and returns in BE format as defined CRB struct.
> - * So saves fault_storage_addr in BE as NX pastes in FIFO and
> - * expects user space to convert to CPU format.
> - */
> - csb.address = crb->stamp.nx.fault_storage_addr;
> - csb.flags = 0;
> -
> - pid = window->task_ref.pid;
> - tsk = get_pid_task(pid, PIDTYPE_PID);
> - /*
> - * Process closes send window after all pending NX requests are
> - * completed. In multi-thread applications, a child thread can
> - * open a window and can exit without closing it. May be some
> - * requests are pending or this window can be used by other
> - * threads later. We should handle faults if NX encounters
> - * pages faults on these requests. Update CSB with translation
> - * error and fault address. If csb_addr passed by user space is
> - * invalid, send SEGV signal to pid saved in window. If the
> - * child thread is not running, send the signal to tgid.
> - * Parent thread (tgid) will close this window upon its exit.
> - *
> - * pid and mm references are taken when window is opened by
> - * process (pid). So tgid is used only when child thread opens
> - * a window and exits without closing it.
> - */
> - if (!tsk) {
> - pid = window->task_ref.tgid;
> - tsk = get_pid_task(pid, PIDTYPE_PID);
> - /*
> - * Parent thread (tgid) will be closing window when it
> - * exits. So should not get here.
> - */
> - if (WARN_ON_ONCE(!tsk))
> - return;
> - }
> -
> - /* Return if the task is exiting. */
> - if (tsk->flags & PF_EXITING) {
> - put_task_struct(tsk);
> - return;
> - }
> -
> - kthread_use_mm(window->task_ref.mm);
> - rc = copy_to_user(csb_addr, &csb, sizeof(csb));
> - /*
> - * User space polls on csb.flags (first byte). So add barrier
> - * then copy first byte with csb flags update.
> - */
> - if (!rc) {
> - csb.flags = CSB_V;
> - /* Make sure update to csb.flags is visible now */
> - smp_mb();
> - rc = copy_to_user(csb_addr, &csb, sizeof(u8));
> - }
> - kthread_unuse_mm(window->task_ref.mm);
> - put_task_struct(tsk);
> -
> - /* Success */
> - if (!rc)
> - return;
> -
> - pr_debug("Invalid CSB address 0x%p signalling pid(%d)\n",
> - csb_addr, pid_vnr(pid));
> -
> - clear_siginfo(&info);
> - info.si_signo = SIGSEGV;
> - info.si_errno = EFAULT;
> - info.si_code = SEGV_MAPERR;
> - info.si_addr = csb_addr;
> -
> - /*
> - * process will be polling on csb.flags after request is sent to
> - * NX. So generally CSB update should not fail except when an
> - * application passes invalid csb_addr. So an error message will
> - * be displayed and leave it to user space whether to ignore or
> - * handle this signal.
> - */
> - rcu_read_lock();
> - rc = kill_pid_info(SIGSEGV, &info, pid);
> - rcu_read_unlock();
> -
> - pr_devel("%s(): pid %d kill_proc_info() rc %d\n", __func__,
> - pid_vnr(pid), rc);
> -}
> -
> static void dump_fifo(struct vas_instance *vinst, void *entry)
> {
> unsigned long *end = vinst->fault_fifo + vinst->fault_fifo_size;
> @@ -272,7 +128,7 @@ irqreturn_t vas_fault_thread_fn(int irq, void *data)
> vinst->vas_id, vinst->fault_fifo, fifo,
> vinst->fault_crbs);
>
> - dump_crb(crb);
> + vas_dump_crb(crb);
> window = vas_pswid_to_window(vinst,
> be32_to_cpu(crb->stamp.nx.pswid));
>
> @@ -293,7 +149,14 @@ irqreturn_t vas_fault_thread_fn(int irq, void *data)
>
> WARN_ON_ONCE(1);
> } else {
> - update_csb(window, crb);
> + /*
> + * NX sees faults only with user space windows.
> + */
> + if (window->user_win)
> + vas_update_csb(crb, &window->task_ref);
> + else
> + WARN_ON_ONCE(!window->user_win);
> +
> /*
> * Return credit for send window after processing
> * fault CRB.
> --
> 2.18.2
>
>
>
