Re: [PATCH 10/35] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS

Dave Hansen
2022-02-09T16:58:43Z

On 1/30/22 13:18, Rick Edgecombe wrote:
>
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index 99d1781fa5f0..75ce4e823902 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -1210,7 +1210,7 @@ static int split_2MB_gtt_entry(struct intel_vgpu *vgpu,
> }
>
> /* Clear dirty field. */
> - se->val64 &= ~_PAGE_DIRTY;
> + se->val64 &= ~_PAGE_DIRTY_BITS;
>
> ops->clear_pse(se);
> ops->clear_ips(se);

Are these x86 CPU page table values? I see ->val64 being used like this:

e->val64 &= ~GEN8_PAGE_PRESENT;
and
se.val64 |= GEN8_PAGE_PRESENT | GEN8_PAGE_RW;

where we also have:

#define GEN8_PAGE_PRESENT BIT_ULL(0)
#define GEN8_PAGE_RW BIT_ULL(1)

Which tells me that these are probably *close* to the CPU's page tables.
But, I honestly don't know which format they are. I don't know if
_PAGE_COW is still a software bit in that format or not.

Either way, I don't think we should be messing with i915 device page tables.

Or, are these somehow magically shared with the CPU in some way I don't
know about?

[ If these are device-only page tables, it would probably be nice to
stop using _PAGE_FOO for them. It would avoid confusion like this. ]