[libvirt] [PATCH 3/3] qemu: Adjust max memlock on mdev hotplug

[Daniel Henrique Barboza]

On 9/3/19 5:09 PM, Eric Farman wrote:
> When starting a domain, we use the presence of a vfio-pci or
> mdev hostdev to determine if the memlock maximum needs to be
> increased.  But if we hotplug either of these devices, only the
> vfio-pci path gets that love.  This means that attaching a, say,
> vfio-ccw device will appear to succeed but the device may be
> unusable as the guest may see I/O errors on long CCW chains.
> The host, meanwhile, would be flooded with these messages:
>
>    vfio_pin_page_external: Task qemu-system-s39 (11584) RLIMIT_MEMLOCK (65536) exceeded
>
> Let's adjust the maximum memlock value in the mdev hotplug path,
> so that the domain has the same value as if it were started with
> one or more mdev devices in its configuration.
>
> (Note: I started trying to refactor qemuDomainAdjustMaxMemLockHostdev()
> to address the "A better way to handle this would be nice" comment,
> but the result was getting way too involved for the problem I was
> trying to fix.  Maybe another day.)
>
> Signed-off-by: Eric Farman <farman at linux.ibm.com>
> ---

Reviewed-by: Daniel Henrique Barboza <danielhb413 at gmail.com>


>   src/qemu/qemu_hotplug.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
> index 979e97b608..ae7c5395d2 100644
> --- a/src/qemu/qemu_hotplug.c
> +++ b/src/qemu/qemu_hotplug.c
> @@ -2755,6 +2755,7 @@ qemuDomainAttachMediatedDevice(virQEMUDriverPtr driver,
>       bool teardowncgroup = false;
>       bool teardownlabel = false;
>       bool teardowndevice = false;
> +    bool teardownmemlock = false;
>       qemuDomainObjPrivatePtr priv = vm->privateData;
>       virDomainDeviceDef dev = { VIR_DOMAIN_DEVICE_HOSTDEV,
>                                   { .hostdev = hostdev } };
> @@ -2798,6 +2799,10 @@ qemuDomainAttachMediatedDevice(virQEMUDriverPtr driver,
>       if (VIR_REALLOC_N(vm->def->hostdevs, vm->def->nhostdevs + 1) < 0)
>           goto cleanup;
>   
> +    if (qemuDomainAdjustMaxMemLockHostdev(vm, hostdev) < 0)
> +        goto cleanup;
> +    teardownmemlock = true;
> +
>       qemuDomainObjEnterMonitor(driver, vm);
>       ret = qemuMonitorAddDevice(priv->mon, devstr);
>       if (qemuDomainObjExitMonitor(driver, vm) < 0) {
> @@ -2813,6 +2818,8 @@ qemuDomainAttachMediatedDevice(virQEMUDriverPtr driver,
>       ret = 0;
>    cleanup:
>       if (ret < 0) {
> +        if (teardownmemlock && qemuDomainAdjustMaxMemLock(vm) < 0)
> +            VIR_WARN("Unable to reset maximum locked memory on hotplug fail");
>           if (teardowncgroup && qemuTeardownHostdevCgroup(vm, hostdev) < 0)
>               VIR_WARN("Unable to remove host device cgroup ACL on hotplug fail");
>           if (teardownlabel &&