On Wed, 12 Jul 2023 03:47:55 +0100, "Aiqun(Maria) Yu" <quic_aiquny@xxxxxxxxxxx> wrote: > > On 7/11/2023 6:38 PM, Marc Zyngier wrote: > > On Tue, 11 Jul 2023 11:12:48 +0100, > > "Aiqun(Maria) Yu" <quic_aiquny@xxxxxxxxxxx> wrote: > >> > >> For the KVM part, per my understanding, as long as the current feature > >> id being overriden, the KVM system also get the current vcpu without > >> the lse atomic feature enabled. > >> KVM vcpu will read the sys reg from host arm64_ftr_regs which is > >> already been controled by the idreg_overrides. > > > > You're completely missing the point. > > > > The guest is free to map memory as non-cacheable *and* to use LSE > > atomics even if the idregs pretend this is not available. At which > The guest also can have the current linux kernel mechanism of LSE > ATOMIC way. [snip useless diagrams] Yes, the guest can do the right thing. The guest, a totally unprivileged piece of SW, can also ignore the idregs and take the whole machine down because your HW is broken. > Just like other KVM vcpu cpu features, lse atomic can be a feature > inherit from the pysical cpu features for the KVM vcpus. See above. Your reasoning applies to a well behaved guest, which is the *wrong* way to reason about these things. M. -- Without deviation from the norm, progress is not possible.
