On 9/29/2014 7:44 PM, Jike Song wrote:
On 09/19/2014 03:25 PM, Chris Wilson wrote:
Now, given that these are simply trapped memory access, wouldn't it be
simply to have:
struct i915_virtual_gpu {
struct vgt_if *if;
} vgu;
static inline bool intel_vgpu_active(struct drm_i915_private *i915) {
return i915->vgpu.if; }
then you have constructs like
void i915_check_vgpu(struct drm_i915_private *i915)
{
struct vgt_if *if;
if = i915->regs + VGT_PVINFO_PAGE;
if (if->magic != VGT_MAGIC)
return;
if (INTEL_VGT_IF_VERSION !=
INTEL_VGT_IF_VERSION_ENCODE(if->version_major,
if->version_minor))
return;
i915->vgpu.if = if;
}
And later, for example:
if (intel_vgpu_active(dev_priv))
dev_priv->num_fence_regs = dev_priv->vgpu.if->fence_num;
Hi Chris, sorry that I didn't understand you correctly. After discussion
with Yu today, I realized that unfortunately, the vgt_if can't be
dereferenced directly.
There are several reasons:
- dereferencing a MMIO address will be complained by sparse(1)
- for Guest VM, such accesses will be trapped by hypervisor, and
hence emulated correctly; However this doesn't work for Host(e.g.
Domain 0 of Xen, the Linux host KVM resides in). For host, we used
a proactive mechanism to redirect i915 MMIO accesses to vgt,
the GPU device-model, for the sake of central management & sharing
among VMs, including host.
Given that, though technically your code works for Guest, but after the
integration of host support of iGVT, we still need to use
I915_READ/I915_WRITE
then. The host patches is soon to posted for your review :)
I should have realized that earlier, sorry!
Hi Chris,
Sorry, I also should have noticed this issue earlier.
To my understanding, the reason you proposed to use the "struct
vgt_if *if" in struct vgpu, to replace the previous vgpu_active, is to
simplify the mmio accesses in our patches. This suggestion works fine
from the guest & native point of view. However, just like Jike's mail
said, this change may not work for the host side, which also need to
visit the PVINFO page from time to time. So, could we still keep the
vgpu_active flag when detecting virtual gpu, and read the mmio registers
in PVINFO structure by I915_READ?
Thanks
Yu
-Chris
--
Thanks,
Jike
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