Re: [Intel-gfx] [PATCH v3 05/28] drm/i915/gvt: Explicitly check that vGPU is attached before shadowing

Sean Christopherson
2023-05-15T17:57:11Z

On Mon, May 15, 2023, Zhi A Wang wrote:
> On 5/13/2023 8:35 AM, Sean Christopherson wrote:
> > Move the check that a vGPU is attacked from is_2MB_gtt_possible() to its
> > sole caller, ppgtt_populate_shadow_entry(). All of the paths in
> > ppgtt_populate_shadow_entry() eventually check for attachment by way of
> > intel_gvt_dma_map_guest_page(), but explicitly checking can avoid
> > unnecessary work and will make it more obvious that a future cleanup of
> > is_2MB_gtt_possible() isn't introducing a bug.
> >
>
> It might be better move this check to shadow_ppgtt_mm() which is used
> in both shadow page table creation and pinning path so that the path
> can bail out even earlier when creating a shadow page table but a vGPU
> has not been attached to KVM yet.

Ah, yes, that'll work. I traced through all of the paths that lead to
ppgtt_populate_shadow_entry(), and shadow_ppgtt_mm() is the only caller that isn't
already gated by INTEL_VGPU_STATUS_ATTACHED or INTEL_VGPU_STATUS_ACTIVE (ACTIVE
is set iff ATTACHED is set).

I'll move the check up to shadow_ppgtt_mm() in the next version.

Thanks!

workload_thread() <= pick_next_workload() => INTEL_VGPU_STATUS_ACTIVE
|
-> dispatch_workload()
|
|-> prepare_workload()
|
-> intel_vgpu_sync_oos_pages()
| |
| |-> ppgtt_set_guest_page_sync()
| |
| |-> sync_oos_page()
| |
| |-> ppgtt_populate_shadow_entry()
|
|-> intel_vgpu_flush_post_shadow()
|
1: |-> ppgtt_handle_guest_write_page_table()
|
|-> ppgtt_handle_guest_entry_add()
|
2: | -> ppgtt_populate_spt_by_guest_entry()
| |
| |-> ppgtt_populate_spt()
| |
| |-> ppgtt_populate_shadow_entry()
| |
| |-> ppgtt_populate_spt_by_guest_entry() [see 2]
|
|-> ppgtt_populate_shadow_entry()

kvmgt_page_track_write() <= KVM callback => INTEL_VGPU_STATUS_ATTACHED
|
|-> intel_vgpu_page_track_handler()
|
|-> ppgtt_write_protection_handler()
|
|-> ppgtt_handle_guest_write_page_table_bytes()
|
|-> ppgtt_handle_guest_write_page_table() [see 1]