gpu: nvgpu: support userspace Read Only mappings

Until now, all userspace buffers were mapped in the GMMU as Read & Write
(RW) by default. In order to enable the use cases which require the GPU
to only read the SYSMEM buffers and not inadvertently write to those,
map buffer ioctls need to provide interface to set the mapping access
type from the userspace.

Some of the use cases are:
  1. A third party server process exposes shared memory that is
     read-only to the client process, which does the GPU processing.
     Registering this memory using cudaHostRegister API as read-only
     in the client process will restict the access to Read Only type
     from the GPU.
  2. IO devices exposing streaming read-only data for processing by
     the GPU.
  3. For marking semantically read-only data as actually read-only
     for the purposes of debugging data corruption.

This patch introduces new AS buffer mapping bitmask flag and
corresponding core VM mapping bitmask flag for representing
Read Only (RO) access type. By default, the access is set
as Read Write (RW).

Bug 200621157

Change-Id: I5ec9dec3ce089e577b86c43003d92b61eee4a90b
Signed-off-by: Sagar Kamble <skamble@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2361750
Reviewed-by: automaticguardword <automaticguardword@nvidia.com>
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit

include/uapi/linux/nvgpu.h

@@ -1918,6 +1918,7 @@ struct nvgpu_as_bind_channel_args {
 #define NVGPU_AS_MAP_BUFFER_FLAGS_L3_ALLOC          (1 << 7)
 #define NVGPU_AS_MAP_BUFFER_FLAGS_DIRECT_KIND_CTRL  (1 << 8)
 #define NVGPU_AS_MAP_BUFFER_FLAGS_PLATFORM_ATOMIC   (1 << 9)
+#define NVGPU_AS_MAP_BUFFER_FLAGS_ACCESS_NO_WRITE   (1 << 10)
 
 /*
  * VM map buffer IOCTL