RE: [PATCH 1/1] iommu/vt-d: Add MTL to quirk list to skip TE disabling

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Thursday, November 16, 2023 3:25 PM
> 
> On 2023/11/16 11:27, Tian, Kevin wrote:
> >> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> >> Sent: Thursday, November 16, 2023 10:23 AM
> >>
> >> @@ -5080,7 +5080,7 @@ static void quirk_igfx_skip_te_disable(struct
> >> pci_dev *dev)
> >>   	ver = (dev->device >> 8) & 0xff;
> >>   	if (ver != 0x45 && ver != 0x46 && ver != 0x4c &&
> >>   	    ver != 0x4e && ver != 0x8a && ver != 0x98 &&
> >> -	    ver != 0x9a && ver != 0xa7)
> >> +	    ver != 0x9a && ver != 0xa7 && ver != 0x7d)
> >>   		return;
> >>
> >
> > this fix alone is fine, but I found this quirk overall is not cleanly handled.
> >
> > Basically it sets iommu_skip_te_disable as true, leading to early return
> > in iommu_disable_translation():
> >
> > 	if (iommu_skip_te_disable && iommu->drhd->gfx_dedicated &&
> > 	   (cap_read_drain(iommu->cap) || cap_write_drain(iommu->cap)))
> > 		return;
> >
> > However the caller of iommu_disable_translation() is not aware of this
> > quirk and continues as if the iommu is disabled. IMHO this is problematic
> > w/o meeting the caller's assumption.
> >
> > e.g. kdump and suspend. We may want to abort those paths early in case
> > of such quirk...
> 
> I can see your point.
> 
> This fix is just to add a new device model to the established quirk
> list. All devices (including the new one) in this quirk list have
> undergone thorough verification. Therefor, I'd like to keep it as-is.
> 
> We can refine the quirk implementation in a separated patch series with
> sufficient consideration and verification. Does this work for you?

sure