Commit 7abc0c6d authored by Greg Kurz's avatar Greg Kurz Committed by David Gibson
Browse files

xics/spapr: Detect old KVM XICS on POWER9 hosts 



Older KVMs on POWER9 don't support destroying/recreating a KVM XICS
device, which is required by 'dual' interrupt controller mode. This
causes QEMU to emit a warning when the guest is rebooted and to fall
back on XICS emulation:

qemu-system-ppc64: warning: kernel_irqchip allowed but unavailable:
 Error on KVM_CREATE_DEVICE for XICS: File exists

If kernel irqchip is required, QEMU will thus exit when the guest is
first rebooted. Failing QEMU this late may be a painful experience
for the user.

Detect that and exit at machine init instead.

Signed-off-by: default avatarGreg Kurz <groug@kaod.org>
Message-Id: <156044430517.125694.6207865998817342638.stgit@bahia.lab.toulouse-stg.fr.ibm.com>
Signed-off-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
parent d9293c48

docs/specs/ppc-spapr-xive.rst

+2 −2
Original line number Diff line number Diff line
@@ -142,8 +142,8 @@ xics XICS KVM XICS emul. XICS KVM 
(3) QEMU fails at CAS with ``Guest requested unavailable interrupt

    mode (XICS), either don't set the ic-mode machine property or try

    ic-mode=xics or ic-mode=dual``

(4) QEMU/KVM incompatibility due to device destruction in reset. This

    needs to be addressed more cleanly with an error.

(4) QEMU/KVM incompatibility due to device destruction in reset. QEMU fails

    with ``KVM is too old to support ic-mode=dual,kernel-irqchip=on``





XIVE Device tree properties

hw/intc/xics_kvm.c

+30 −0
Original line number Diff line number Diff line
@@ -452,3 +452,33 @@ void xics_kvm_disconnect(SpaprMachineState *spapr, Error **errp) 
    /* Clear the presenter from the VCPUs */

    kvm_disable_icps();

}



/*

 * This is a heuristic to detect older KVMs on POWER9 hosts that don't

 * support destruction of a KVM XICS device while the VM is running.

 * Required to start a spapr machine with ic-mode=dual,kernel-irqchip=on.

 */

bool xics_kvm_has_broken_disconnect(SpaprMachineState *spapr)

{

    int rc;



    rc = kvm_create_device(kvm_state, KVM_DEV_TYPE_XICS, false);

    if (rc < 0) {

        /*

         * The error is ignored on purpose. The KVM XICS setup code

         * will catch it again anyway. The goal here is to see if

         * close() actually destroys the device or not.

         */

        return false;

    }



    close(rc);



    rc = kvm_create_device(kvm_state, KVM_DEV_TYPE_XICS, false);

    if (rc >= 0) {

        close(rc);

        return false;

    }



    return errno == EEXIST;

}

hw/ppc/spapr_irq.c

+13 −0
Original line number Diff line number Diff line
@@ -669,6 +669,19 @@ static void spapr_irq_check(SpaprMachineState *spapr, Error **errp) 
            return;

        }

    }



    /*

     * On a POWER9 host, some older KVM XICS devices cannot be destroyed and

     * re-created. Detect that early to avoid QEMU to exit later when the

     * guest reboots.

     */

    if (kvm_enabled() &&

        spapr->irq == &spapr_irq_dual &&

        machine_kernel_irqchip_required(machine) &&

        xics_kvm_has_broken_disconnect(spapr)) {

        error_setg(errp, "KVM is too old to support ic-mode=dual,kernel-irqchip=on");

        return;

    }

}



/*

include/hw/ppc/xics_spapr.h

+1 −0
Original line number Diff line number Diff line
@@ -35,6 +35,7 @@ void spapr_dt_xics(SpaprMachineState *spapr, uint32_t nr_servers, void *fdt, 
                   uint32_t phandle);

int xics_kvm_init(SpaprMachineState *spapr, Error **errp);

void xics_kvm_disconnect(SpaprMachineState *spapr, Error **errp);

bool xics_kvm_has_broken_disconnect(SpaprMachineState *spapr);

void xics_spapr_init(SpaprMachineState *spapr);

void xics_spapr_connect(SpaprMachineState *spapr);