Re: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory

[Marc Zyngier]

On Tue, 05 Dec 2023 17:33:01 +0000,
Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
> 
> On Tue, Dec 05, 2023 at 05:01:28PM +0000, Marc Zyngier wrote:
> > On Tue, 05 Dec 2023 16:43:18 +0000,
> > Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
> > > On Tue, Dec 05, 2023 at 04:22:33PM +0000, Catalin Marinas wrote:
> > > > That's an argument to restrict this feature to PCIe. It's really about
> > > > fewer arguments on the behaviour of other devices. Marc did raise
> > > > another issue with the GIC VCPU interface (does this even have a vma in
> > > > the host VMM?). That's a class of devices where the mapping is
> > > > context-switched, so the TLBI+DSB rules don't help.
> > 
> > There is no vma. The CPU interface is entirely under control of KVM.
> > Userspace only provides the IPA for the mapping.
> 
> That's good to know. We can solve the GIC issue by limiting the
> relaxation to those mappings that have a user vma.

Yes, this should definitely be part of the decision.

> Ideally we should do this for vfio only but we don't have an easy
> way to convey this to KVM.

But if we want to limit this to PCIe, we'll have to find out. The
initial proposal (a long while ago) had a flag conveying some
information, and I'd definitely feel more confident having something
like that.

	M.

-- 
Without deviation from the norm, progress is not possible.