drm/vmwgfx: Fix prime with external buffers

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/vmwgfx: Fix prime with external buffers Make sure that for external buffers mapping goes through the dma_buf interface instead of trying to access pages directly. External buffers might not provide direct access to readable/writable pages so to make sure the bo's created from external dma_bufs can be read dma_buf interface has to be used. Fixes crashes in IGT's kms_prime with vgem. Regular desktop usage won't trigger this due to the fact that virtual machines will not have multiple GPUs but it enables better test coverage in IGT.

References

• https://git.kernel.org/stable/c/9a9716bbbf3dd6b6cbefba3abcc89af8b72631f4
• https://git.kernel.org/stable/c/5c12391ee1ab59cb2f3be3f1f5e6d0fc0c2dc854
• https://git.kernel.org/stable/c/50f1199250912568606b3778dc56646c10cb7b04