On Wed, May 15, 2024, Rick P Edgecombe wrote: > On Wed, 2024-05-15 at 12:48 -0700, Sean Christopherson wrote: > > > It's just another little quirk in an already complicated solution. They > > > third > > > thing we discussed was somehow rejecting or not supporting non-coherent DMA. > > > This seemed simpler than that. > > > > Again, huh? This has _nothing_ to do with non-coherent DMA. Devices can't > > DMA > > into TDX private memory. > > Hmm... I'm confused how you are confused... :) > > For normal VMs (after that change you linked), guests will honor guest PAT on > newer HW. On older HW it will only honor guest PAT if non-coherent DMA is > attached. > > For TDX we can't honor guest PAT for private memory. So we can either have: > 1. Have shared honor PAT and private not. > 2. Have private and shared both not honor PAT and be consistent. Unless non- > coherent DMA is attached. In that case KVM could zap shared only and switch to > 1. Oh good gravy, hell no :-)
