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    SubjectRe: [PATCH] x86: kvm: reset the bootstrap processor when it gets an INIT
    On Mon, Mar 11, 2013 at 12:25:57PM +0100, Paolo Bonzini wrote:
    > Il 11/03/2013 11:28, Gleb Natapov ha scritto:
    > >> Not really true---we do exit with that state and EINTR when we get a
    > >> SIPI. Perhaps that can be changed.
    > >
    > > That's implementation detail. We can jump to the beginning of the
    > > function instead. Nowhere we document that entering
    > > KVM_MP_STATE_SIPI_RECEIVED state cause KVM_RUN return with EINTR.
    >
    > Yes, that would be nice.
    >
    That's not performance critical path, so I guess no one bothered.

    > >>> If AP is hard reset
    > >>> userspase makes it UNINIT, if soft reset it makes it INIT_RECEIVED, if
    > >>> BSP it makes it running no matter what type of reset.
    > >>
    > >> The current name just suggests .
    > >> And when getting an INIT in the in-kernel LAPIC, this:
    > >>
    > >> - vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
    > >> + vcpu->arch.mp_state = kvm_vcpu_is_bsp(vcpu) ?
    > >> + KVM_MP_STATE_SIPI_RECEIVED :
    > >> + KVM_MP_STATE_INIT_RECEIVED;
    > >>
    > >> makes much less sense than this:
    > >>
    > >> - vcpu->arch.mp_state = KVM_MP_STATE_WAIT_FOR_SIPI;
    > >> + vcpu->arch.mp_state = kvm_vcpu_is_bsp(vcpu) ?
    > >> + KVM_MP_STATE_RESET_NOW :
    > >> + KVM_MP_STATE_WAIT_FOR_SIPI;
    > >>
    > > Both of them are equally incorrect. INIT should cause reset, and only if
    > > vmx is off. An userspace reset is also completely broken in that regard.
    > > Renaming things gives us nothing, only bring unneeded churn. If the
    > > names were internal I wouldn't mind, but they are APIs.
    > >
    > >> However, there's also Jan's plans for nVMX. Peeking at his queue (see
    > >> http://git.kiszka.org/?p=linux-kvm.git;a=commitdiff;h=037fb24ec) I think
    > >> it's better to always reflect INITs to the hypervisor like I did in these
    > >> patches.
    > >>
    > > The commit was before we decided that we should not abuse mp_state for
    > > signaling.
    >
    > Agreed, but we still have the problem of how to signal from userspace.
    > For that do you have any other suggestion than mp_state? And if we keep
    > mp_state to signal from userspace, giving INIT_RECEIVED the
    > "wait-for-SIPI" semantics would be wrong.
    >
    I don't see how can we use mp_state for signaling from userspace either.
    Currently soft reset always reset vcpus, so it is OK for userspace to
    generate reset vcpu state and put it into kernel, mp_state is just one
    of the updated states, but when INIT will be just another signal that
    may or may not reset cpu or have other side effects like #vmexit this
    will not longer work. We will have to have another interface for
    injecting INIT from userspace and userspace soft-reset will use it
    instead of doing reset by itself.

    --
    Gleb.


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