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Subject[PATCH v5 5/9] drm/ttm: TTM fault handler helpers
Date
From: Thomas Hellstrom <thellstrom@vmware.com>

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>
Reviewed-by: "Christian König" <christian.koenig@amd.com> #v1
---
drivers/gpu/drm/ttm/ttm_bo_vm.c | 175 +++++++++++++++++++-------------
include/drm/ttm/ttm_bo_api.h | 10 ++
2 files changed, 113 insertions(+), 72 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 196e13a0adad..2d9862fcf6fd 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 +148,55 @@ 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
+ * @prot: The page protection to be used for this memory area.
+ * @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,
+ pgprot_t prot,
+ pgoff_t num_prefault)
+{
+ 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;
+ 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 +207,9 @@ 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) {
@@ -189,26 +225,15 @@ 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;
- goto out_io_unlock;
- }
+ if (unlikely(err != 0))
+ return VM_FAULT_SIGBUS;

page_offset = ((address - vma->vm_start) >> PAGE_SHIFT) +
vma->vm_pgoff - drm_vma_node_start(&bo->vma_node);
@@ -220,18 +245,8 @@ 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);
-
- if (bo->mem.bus.is_iomem) {
- cvma.vm_page_prot = ttm_io_prot(bo->mem.placement,
- cvma.vm_page_prot);
- } else {
+ cvma.vm_page_prot = ttm_io_prot(bo->mem.placement, prot);
+ if (!bo->mem.bus.is_iomem) {
struct ttm_operation_ctx ctx = {
.interruptible = false,
.no_wait_gpu = false,
@@ -240,24 +255,21 @@ 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);
-
- /* Allocate all page at once, most common usage */
- if (ttm_tt_populate(ttm, &ctx)) {
+ if (ttm_tt_populate(bo->ttm, &ctx)) {
ret = VM_FAULT_OOM;
goto out_io_unlock;
}
+ } else {
+ /* Iomem should not be marked encrypted */
+ cvma.vm_page_prot = pgprot_decrypted(cvma.vm_page_prot);
}

/*
* 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);
pfn = ttm_bo_io_mem_pfn(bo, page_offset);
} else {
page = ttm->pages[page_offset];
@@ -295,7 +307,26 @@ 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;
+ pgprot_t prot;
+ struct ttm_buffer_object *bo = vma->vm_private_data;
+ vm_fault_t ret;
+
+ ret = ttm_bo_vm_reserve(bo, vmf);
+ if (ret)
+ return ret;
+
+ prot = vm_get_page_prot(vma->vm_flags);
+ ret = ttm_bo_vm_fault_reserved(vmf, prot, 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..435d02f719a8 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,
+ pgprot_t prot,
+ pgoff_t num_prefault);
#endif
--
2.20.1
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