Excerpts from Haren Myneni's message of February 20, 2022 5:55 am:
>
> The user space opens VAS windows and issues NX requests by pasting
> CRB on the corresponding paste address mmap. When the system lost
> credits due to core removal, the kernel has to close the window in
> the hypervisor and make the window inactive by unmapping this paste
> address. Also the OS has to handle NX request page faults if the user
> space issue NX requests.
>
> This handler maps the new paste address with the same VMA when the
> window is active again (due to core add with DLPAR). Otherwise
> returns paste failure.
>
Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> Signed-off-by: Haren Myneni <ha...@linux.ibm.com>
> ---
> arch/powerpc/include/asm/vas.h | 10 ++++
> arch/powerpc/platforms/book3s/vas-api.c | 68 +++++++++++++++++++++++++
> 2 files changed, 78 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/vas.h b/arch/powerpc/include/asm/vas.h
> index 57573d9c1e09..27251af18c65 100644
> --- a/arch/powerpc/include/asm/vas.h
> +++ b/arch/powerpc/include/asm/vas.h
> @@ -29,6 +29,12 @@
> #define VAS_THRESH_FIFO_GT_QTR_FULL 2
> #define VAS_THRESH_FIFO_GT_EIGHTH_FULL 3
>
> +/*
> + * VAS window Linux status bits
> + */
> +#define VAS_WIN_ACTIVE 0x0 /* Used in platform independent
> */
> + /* vas mmap() */
> +
> /*
> * Get/Set bit fields
> */
> @@ -59,6 +65,9 @@ struct vas_user_win_ref {
> struct pid *pid; /* PID of owner */
> struct pid *tgid; /* Thread group ID of owner */
> struct mm_struct *mm; /* Linux process mm_struct */
> + struct mutex mmap_mutex; /* protects paste address mmap() */
> + /* with DLPAR close/open windows */
> + struct vm_area_struct *vma; /* Save VMA and used in DLPAR ops */
> };
>
> /*
> @@ -67,6 +76,7 @@ struct vas_user_win_ref {
> struct vas_window {
> u32 winid;
> u32 wcreds_max; /* Window credits */
> + u32 status; /* Window status used in OS */
> enum vas_cop_type cop;
> struct vas_user_win_ref task_ref;
> char *dbgname;
> diff --git a/arch/powerpc/platforms/book3s/vas-api.c
> b/arch/powerpc/platforms/book3s/vas-api.c
> index 4d82c92ddd52..f359e7b2bf90 100644
> --- a/arch/powerpc/platforms/book3s/vas-api.c
> +++ b/arch/powerpc/platforms/book3s/vas-api.c
> @@ -316,6 +316,7 @@ static int coproc_ioc_tx_win_open(struct file *fp,
> unsigned long arg)
> return PTR_ERR(txwin);
> }
>
> + mutex_init(&txwin->task_ref.mmap_mutex);
> cp_inst->txwin = txwin;
>
> return 0;
> @@ -350,6 +351,70 @@ static int coproc_release(struct inode *inode, struct
> file *fp)
> return 0;
> }
>
> +/*
> + * This fault handler is invoked when the core generates page fault on
> + * the paste address. Happens if the kernel closes window in hypervisor
> + * (on pseries) due to lost credit or the paste address is not mapped.
> + */
> +static vm_fault_t vas_mmap_fault(struct vm_fault *vmf)
> +{
> + struct vm_area_struct *vma = vmf->vma;
> + struct file *fp = vma->vm_file;
> + struct coproc_instance *cp_inst = fp->private_data;
> + struct vas_window *txwin;
> + u64 paste_addr;
> + int ret;
> +
> + /*
> + * window is not opened. Shouldn't expect this error.
> + */
> + if (!cp_inst || !cp_inst->txwin) {
> + pr_err("%s(): Unexpected fault on paste address with TX window
> closed\n",
> + __func__);
> + return VM_FAULT_SIGBUS;
> + }
> +
> + txwin = cp_inst->txwin;
> + /*
> + * When the LPAR lost credits due to core removal or during
> + * migration, invalidate the existing mapping for the current
> + * paste addresses and set windows in-active (zap_page_range in
> + * reconfig_close_windows()).
> + * New mapping will be done later after migration or new credits
> + * available. So continue to receive faults if the user space
> + * issue NX request.
> + */
> + if (txwin->task_ref.vma != vmf->vma) {
> + pr_err("%s(): No previous mapping with paste address\n",
> + __func__);
> + return VM_FAULT_SIGBUS;
> + }
> +
> + mutex_lock(&txwin->task_ref.mmap_mutex);
> + /*
> + * The window may be inactive due to lost credit (Ex: core
> + * removal with DLPAR). If the window is active again when
> + * the credit is available, map the new paste address at the
> + * the window virtual address.
> + */
> + if (txwin->status == VAS_WIN_ACTIVE) {
> + paste_addr = cp_inst->coproc->vops->paste_addr(txwin);
> + if (paste_addr) {
> + ret = vmf_insert_pfn(vma, vma->vm_start,
> + (paste_addr >> PAGE_SHIFT));
> + mutex_unlock(&txwin->task_ref.mmap_mutex);
> + return ret;
> + }
> + }
> + mutex_unlock(&txwin->task_ref.mmap_mutex);
> +
> + return VM_FAULT_SIGBUS;
> +
> +}
> +static const struct vm_operations_struct vas_vm_ops = {
> + .fault = vas_mmap_fault,
> +};
> +
> static int coproc_mmap(struct file *fp, struct vm_area_struct *vma)
> {
> struct coproc_instance *cp_inst = fp->private_data;
> @@ -398,6 +463,9 @@ static int coproc_mmap(struct file *fp, struct
> vm_area_struct *vma)
> pr_devel("%s(): paste addr %llx at %lx, rc %d\n", __func__,
> paste_addr, vma->vm_start, rc);
>
> + txwin->task_ref.vma = vma;
> + vma->vm_ops = &vas_vm_ops;
> +
> return rc;
> }
>
> --
> 2.27.0
>
>
>
