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SubjectRe: [PATCH 5/9] drm/ttm: TTM fault handler helpers
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Am 12.04.19 um 18:04 schrieb Thomas Hellstrom:
> With the vmwgfx dirty tracking, the default TTM fault handler is not
> completely sufficient (vmwgfx need to modify the vma->vm_flags member,
> and also needs to restrict the number of prefaults).
>
> We also want to replicate the new ttm_bo_vm_reserve() functionality
>
> So start turning the TTM vm code into helpers: ttm_bo_vm_fault_reserved()
> and ttm_bo_vm_reserve(), and provide a default TTM fault handler for other
> drivers to use.
>
> Cc: "Christian König" <christian.koenig@amd.com>
> Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>

Two nit picks below, apart from that looks good to me as well.

> ---
> drivers/gpu/drm/ttm/ttm_bo_vm.c | 170 ++++++++++++++++++++------------
> include/drm/ttm/ttm_bo_api.h | 10 ++
> 2 files changed, 116 insertions(+), 64 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index bfb25b81fed7..3bd28fb97124 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -42,8 +42,6 @@
> #include <linux/uaccess.h>
> #include <linux/mem_encrypt.h>
>
> -#define TTM_BO_VM_NUM_PREFAULT 16
> -
> static vm_fault_t ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
> struct vm_fault *vmf)
> {
> @@ -106,31 +104,30 @@ static unsigned long ttm_bo_io_mem_pfn(struct ttm_buffer_object *bo,
> + page_offset;
> }
>
> -static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> +/**
> + * ttm_bo_vm_reserve - Reserve a buffer object in a retryable vm callback
> + * @bo: The buffer object
> + * @vmf: The fault structure handed to the callback
> + *
> + * vm callbacks like fault() and *_mkwrite() allow for the mm_sem to be dropped
> + * during long waits, and after the wait the callback will be restarted. This
> + * is to allow other threads using the same virtual memory space concurrent
> + * access to map(), unmap() completely unrelated buffer objects. TTM buffer
> + * object reservations sometimes wait for GPU and should therefore be
> + * considered long waits. This function reserves the buffer object interruptibly
> + * taking this into account. Starvation is avoided by the vm system not
> + * allowing too many repeated restarts.
> + * This function is intended to be used in customized fault() and _mkwrite()
> + * handlers.
> + *
> + * Return:
> + * 0 on success and the bo was reserved.
> + * VM_FAULT_RETRY if blocking wait.
> + * VM_FAULT_NOPAGE if blocking wait and retrying was not allowed.
> + */
> +vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
> + struct vm_fault *vmf)
> {
> - struct vm_area_struct *vma = vmf->vma;
> - struct ttm_buffer_object *bo = (struct ttm_buffer_object *)
> - vma->vm_private_data;
> - struct ttm_bo_device *bdev = bo->bdev;
> - unsigned long page_offset;
> - unsigned long page_last;
> - unsigned long pfn;
> - struct ttm_tt *ttm = NULL;
> - struct page *page;
> - int err;
> - int i;
> - vm_fault_t ret = VM_FAULT_NOPAGE;
> - unsigned long address = vmf->address;
> - struct ttm_mem_type_manager *man =
> - &bdev->man[bo->mem.mem_type];
> - struct vm_area_struct cvma;
> -
> - /*
> - * Work around locking order reversal in fault / nopfn
> - * between mmap_sem and bo_reserve: Perform a trylock operation
> - * for reserve, and if it fails, retry the fault after waiting
> - * for the buffer to become unreserved.
> - */
> if (unlikely(!reservation_object_trylock(bo->resv))) {
> if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
> if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
> @@ -151,14 +148,56 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> return VM_FAULT_NOPAGE;
> }
>
> + return 0;
> +}
> +EXPORT_SYMBOL(ttm_bo_vm_reserve);
> +
> +/**
> + * ttm_bo_vm_fault_reserved - TTM fault helper
> + * @vmf: The struct vm_fault given as argument to the fault callback
> + * @cvma: The struct vmw_area_struct affected. Note that this may be a
> + * copy of the real vma object if the caller needs, for example, VM
> + * flags to be temporarily altered while determining the page protection.
> + * @num_prefault: Maximum number of prefault pages. The caller may want to
> + * specify this based on madvice settings and the size of the GPU object
> + * backed by the memory.
> + *
> + * This function inserts one or more page table entries pointing to the
> + * memory backing the buffer object, and then returns a return code
> + * instructing the caller to retry the page access.
> + *
> + * Return:
> + * VM_FAULT_NOPAGE on success or pending signal
> + * VM_FAULT_SIGBUS on unspecified error
> + * VM_FAULT_OOM on out-of-memory
> + * VM_FAULT_RETRY if retryable wait
> + */
> +vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> + struct vm_area_struct *cvma,
> + pgoff_t num_prefault)
> +{
> + struct vm_area_struct *vma = vmf->vma;
> + struct ttm_buffer_object *bo = (struct ttm_buffer_object *)
> + vma->vm_private_data;
> + struct ttm_bo_device *bdev = bo->bdev;
> + unsigned long page_offset;
> + unsigned long page_last;
> + unsigned long pfn;
> + struct ttm_tt *ttm = NULL;
> + struct page *page;
> + int err;
> + pgoff_t i;
> + vm_fault_t ret = VM_FAULT_NOPAGE;
> + unsigned long address = vmf->address;
> + struct ttm_mem_type_manager *man =
> + &bdev->man[bo->mem.mem_type];
> +
> /*
> * Refuse to fault imported pages. This should be handled
> * (if at all) by redirecting mmap to the exporter.
> */
> - if (bo->ttm && (bo->ttm->page_flags & TTM_PAGE_FLAG_SG)) {
> - ret = VM_FAULT_SIGBUS;
> - goto out_unlock;
> - }
> + if (bo->ttm && (bo->ttm->page_flags & TTM_PAGE_FLAG_SG))
> + return VM_FAULT_SIGBUS;
>
> if (bdev->driver->fault_reserve_notify) {
> struct dma_fence *moving = dma_fence_get(bo->moving);
> @@ -169,11 +208,9 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> break;
> case -EBUSY:
> case -ERESTARTSYS:
> - ret = VM_FAULT_NOPAGE;
> - goto out_unlock;
> + return VM_FAULT_NOPAGE;
> default:
> - ret = VM_FAULT_SIGBUS;
> - goto out_unlock;
> + return VM_FAULT_SIGBUS;
> }
>
> if (bo->moving != moving) {
> @@ -189,24 +226,15 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> * move.
> */
> ret = ttm_bo_vm_fault_idle(bo, vmf);
> - if (unlikely(ret != 0)) {
> - if (ret == VM_FAULT_RETRY &&
> - !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
> - /* The BO has already been unreserved. */
> - return ret;
> - }
> -
> - goto out_unlock;
> - }
> + if (unlikely(ret != 0))
> + return ret;
>
> err = ttm_mem_io_lock(man, true);
> - if (unlikely(err != 0)) {
> - ret = VM_FAULT_NOPAGE;
> - goto out_unlock;
> - }
> + if (unlikely(err != 0))
> + return VM_FAULT_NOPAGE;
> err = ttm_mem_io_reserve_vm(bo);
> if (unlikely(err != 0)) {
> - ret = VM_FAULT_SIGBUS;
> + return VM_FAULT_SIGBUS;
> goto out_io_unlock;

This goto is now superfluous.

> }
>
> @@ -220,17 +248,11 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> goto out_io_unlock;
> }
>
> - /*
> - * Make a local vma copy to modify the page_prot member
> - * and vm_flags if necessary. The vma parameter is protected
> - * by mmap_sem in write mode.
> - */
> - cvma = *vma;
> - cvma.vm_page_prot = vm_get_page_prot(cvma.vm_flags);
> + cvma->vm_page_prot = vm_get_page_prot(cvma->vm_flags);
>
> if (bo->mem.bus.is_iomem) {
> - cvma.vm_page_prot = ttm_io_prot(bo->mem.placement,
> - cvma.vm_page_prot);
> + cvma->vm_page_prot = ttm_io_prot(bo->mem.placement,
> + cvma->vm_page_prot);
> } else {
> struct ttm_operation_ctx ctx = {
> .interruptible = false,
> @@ -240,8 +262,8 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> };
>
> ttm = bo->ttm;
> - cvma.vm_page_prot = ttm_io_prot(bo->mem.placement,
> - cvma.vm_page_prot);
> + cvma->vm_page_prot = ttm_io_prot(bo->mem.placement,
> + cvma->vm_page_prot);
>
> /* Allocate all page at once, most common usage */
> if (ttm_tt_populate(ttm, &ctx)) {
> @@ -254,10 +276,11 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> * Speculatively prefault a number of pages. Only error on
> * first page.
> */
> - for (i = 0; i < TTM_BO_VM_NUM_PREFAULT; ++i) {
> + for (i = 0; i < num_prefault; ++i) {
> if (bo->mem.bus.is_iomem) {
> /* Iomem should not be marked encrypted */
> - cvma.vm_page_prot = pgprot_decrypted(cvma.vm_page_prot);
> + cvma->vm_page_prot =
> + pgprot_decrypted(cvma->vm_page_prot);
> pfn = ttm_bo_io_mem_pfn(bo, page_offset);
> } else {
> page = ttm->pages[page_offset];
> @@ -273,10 +296,10 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> }
>
> if (vma->vm_flags & VM_MIXEDMAP)
> - ret = vmf_insert_mixed(&cvma, address,
> + ret = vmf_insert_mixed(cvma, address,
> __pfn_to_pfn_t(pfn, PFN_DEV));
> else
> - ret = vmf_insert_pfn(&cvma, address, pfn);
> + ret = vmf_insert_pfn(cvma, address, pfn);
>
> /*
> * Somebody beat us to this PTE or prefaulting to
> @@ -295,7 +318,26 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> ret = VM_FAULT_NOPAGE;
> out_io_unlock:
> ttm_mem_io_unlock(man);
> -out_unlock:
> + return ret;
> +}
> +EXPORT_SYMBOL(ttm_bo_vm_fault_reserved);
> +
> +static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> +{
> + struct vm_area_struct *vma = vmf->vma;
> + struct vm_area_struct cvma = *vma;
> + struct ttm_buffer_object *bo = (struct ttm_buffer_object *)
> + vma->vm_private_data;

That extra cast can be dropped, the vm_private_data member is a void*
anyway.

Regards,
Christian.

> + vm_fault_t ret;
> +
> + ret = ttm_bo_vm_reserve(bo, vmf);
> + if (ret)
> + return ret;
> +
> + ret = ttm_bo_vm_fault_reserved(vmf, &cvma, TTM_BO_VM_NUM_PREFAULT);
> + if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
> + return ret;
> +
> reservation_object_unlock(bo->resv);
> return ret;
> }
> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> index 49d9cdfc58f2..bebfa16426ca 100644
> --- a/include/drm/ttm/ttm_bo_api.h
> +++ b/include/drm/ttm/ttm_bo_api.h
> @@ -768,4 +768,14 @@ int ttm_bo_swapout(struct ttm_bo_global *glob,
> struct ttm_operation_ctx *ctx);
> void ttm_bo_swapout_all(struct ttm_bo_device *bdev);
> int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo);
> +
> +/* Default number of pre-faulted pages in the TTM fault handler */
> +#define TTM_BO_VM_NUM_PREFAULT 16
> +
> +vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
> + struct vm_fault *vmf);
> +
> +vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> + struct vm_area_struct *cvma,
> + pgoff_t num_prefault);
> #endif

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