Re: [PATCH v4 0/8] Add enlightenments for vGPU

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 02/10/2015 11:05 AM, Yu Zhang wrote:
> This patch set includes necessary code changes when i915 driver
> runs inside a VM. Though ideally we can run an unmodified i915
> driver in VM, adding such enlightenments can greatly reduce the
> virtualization complexity in orders of magnitude. Code changes
> for the host side, which includes the actual Intel GVT-g
> implementation, will be sent out in other patches.
>
> The primary change introduced here is to implement so-called
> "address space ballooning" technique. XenGT partitions global
> graphics memory among multiple VMs, so each VM can directly
> access a portion of the memory without hypervisor's intervention,
> e.g. filling textures or queuing commands. However with the
> partitioning an unmodified i915 driver would assume a smaller
> graphics memory starting from address ZERO, so requires XenGT
> core module (vgt) to translate the graphics address between
> 'guest view' and 'host view', for all registers and command
> opcodes which contain a graphics memory address. To reduce the
> complexity, XenGT introduces "address space ballooning", by
> telling the exact partitioning knowledge to each guest i915
> driver, which then reserves and prevents non-allocated portions
> from allocation. Then vgt module only needs to scan and validate
> graphics addresses without complexity of translation.
>
> Note: The partitioning of global graphics memory may break some
> applications, with large objects in the aperture, because current
> userspace assumes half of the aperture usable. That would need
> separate fix either in user space (e.g. remove assumption in mesa)
> or in kernel (with some faulting mechanism).
>
> The partitioning knowledge is conveyed through a reserved MMIO
> range, called PVINFO, which will be architecturally reserved in
> future hardware generations. Another information carried through
> PVINFO is about the number of fence registers. As a global resource,
> XenGT also partitions them among VMs.
>
> Other changes are trivial as optimizations, to either reduce the
> trap overhead or disable power management features which don't
> make sense in a virtualized environment.
>
>
> Yu Zhang (8):
>    drm/i915: Introduce a PV INFO page structure for Intel GVT-g.
>    drm/i915: Adds graphic address space ballooning logic
>    drm/i915: Partition the fence registers for vGPU in i915 driver
>    drm/i915: Disable framebuffer compression for i915 driver in VM
>    drm/i915: Add the display switch logic for vGPU in i915 driver
>    drm/i915: Disable power management for i915 driver in VM
>    drm/i915: Create vGPU specific MMIO operations to reduce traps
>    drm/i915: Support alias ppgtt in VM if ppgtt is enabled

All my comments have been addressed (and I especially like the ASCII 
diagram of the memory space!) so you can put my r-b on all the patches 
from this series:

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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