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

["Yu, Zhang" <yu.c.zhang@linux.intel.com>]

On 2/11/2015 4:06 PM, Daniel Vetter wrote:
> On Tue, Feb 10, 2015 at 12:11:02PM +0000, Tvrtko Ursulin wrote:
>> 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>
>
> All merged, thanks for patches&review.
> -Daniel
Got it. Thank you, Daniel! :)

Yu
>
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