This is neccessary as e.g. shaders can be updated through a mirror and never hit modification traps. By tracking which addresses have sequenced writes applied, the shader manager can then correctly detect if a given shader has been modified by the GPU.
Previously, both I2M uploads and DMA copies would force GPU serialisation if they happened to hit a trap or were used to copy GPU dirty buffers. By using the buffer manager to implement them on the host GPU we can avoid such slowdowns entiely.
