On Tue, Nov 13, 2018 at 7:16 PM Christoffer Dall <christoffer.dall@xxxxxxx> wrote: > > On Mon, Nov 12, 2018 at 10:32:12PM +0000, Catalin Marinas wrote: > > On Fri, Nov 02, 2018 at 09:37:25AM +0100, Christoffer Dall wrote: > > > On Wed, Oct 17, 2018 at 04:17:55PM +0530, Amit Daniel Kachhap wrote: > > > > From: Mark Rutland <mark.rutland@xxxxxxx> > > > > > > > > When pointer authentication is supported, a guest may wish to use it. > > > > This patch adds the necessary KVM infrastructure for this to work. > > > > > > > > When we schedule a vcpu, we enable guest usage of pointer > > > > authentication instructions and accesses to the keys. After these are > > > > enabled, we allow context-switching the keys. > > > > > > > > Pointer authentication consists of address authentication and generic > > > > authentication, and CPUs in a system might have varied support for > > > > either. Where support for either feature is not uniform, it is hidden > > > > from guests via ID register emulation, as a result of the cpufeature > > > > framework in the host. > > > > > > > > Unfortunately, address authentication and generic authentication cannot > > > > be trapped separately, as the architecture provides a single EL2 trap > > > > covering both. If we wish to expose one without the other, we cannot > > > > prevent a (badly-written) guest from intermittently using a feature > > > > which is not uniformly supported (when scheduled on a physical CPU which > > > > supports the relevant feature). When the guest is scheduled on a > > > > physical CPU lacking the feature, these attempts will result in an UNDEF > > > > being taken by the guest. > > > > > > > > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> > > > > Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx> > > > > Cc: Marc Zyngier <marc.zyngier@xxxxxxx> > > > > Cc: Christoffer Dall <christoffer.dall@xxxxxxx> > > > > Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx > > [...] > > > Two questions: > > > > > > - Can we limit all ptrauth functionality to VHE systems so that we > > > don't need to touch the non-VHE path and so that we don't need any of > > > the __hyp_text stuff? > > > > I would say yes. ARMv8.3 implies v8.1, so can enable ptrauth only when > > VHE is built into the kernel and present in the CPU implementation. > > > > Sounds good. > > > > - Can we move all the save/restore logic to vcpu load/put as long as > > > the host kernel itself isn't using ptrauth, and if the host kernel at > > > some point begins to use ptrauth, can we have a hook to save/restore > > > at that time (similar to what we do for FPSIMD) to avoid this > > > overhead on every switch? > > > > We will probably enable ptrauth for the kernel as well fairly soon, so I > > don't think we should base the KVM assumption on the no ptrauth in > > kernel use-case. > > > > I assume in this case ptrauth will be used for all of the kernel, > including most of the KVM code? > > In that case, I wonder if we always need to context-switch ptrauth > configruation state or if we can be lazy until the guest actually uses > the feature? Sorry for the delayed reply. Lazy switching is possible and was present in earlier Mark's Rutland v2 version. However removed it from v3 version as a mandatory user option to enable ptrauth is added and to make it look simpler. But yes both can exist together but with 1 trap cost if guest always uses ptrauth. Thanks, Amit > > > Thanks, > > Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
