On Thu, 2 Mar 2023 at 14:29, Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > > On Thu, Mar 02 2023, Peter Maydell <peter.maydell@xxxxxxxxxx> wrote: > > I think having MTE in the specific case of KVM behave differently > > to how we've done all these existing properties and how we've > > done MTE for TCG would be confusing. The simplest thing is to just > > follow the existing UI for TCG MTE. > > > > The underlying reason for this is that MTE in general is not a feature > > only of the CPU, but also of the whole system design. It happens > > that KVM gives us tagged RAM "for free" but that's an oddity > > of the KVM implementation -- in real hardware there needs to > > be system level support for tagging. > > Hm... the Linux kernel actually seems to consider MTE to be a cpu > feature (at least, it lists it in the cpu features). > > So, is your suggestion to use the 'mte' prop of the virt machine to mean > "enable all prereqs for MTE, i.e. allocate tag memory for TCG and enable > MTE in the kernel for KVM"? For TCG, we'll get MTE for the max cpu > model; for KVM, we'd get MTE for host (== max), but I'm wondering what > should happen if we get named cpu models and the user specifies one > where we won't have MTE (i.e. some pre-8.5 one)? I think we can probably cross that bridge when we get to it, but I imagine the semantics would be "cortex-foo plus MTE" (in the same way that -cpu cortex-foo,+x,-y can add and subtract features from a baseline). thanks -- PMM
