[PATCH v3 11/14] qemuDomainSetMemoryFlags: Take virtio-mem into consideration

[Peter Krempa]

On Fri, Apr 23, 2021 at 15:24:33 +0200, Michal Privoznik wrote:
> The qemuDomainSetMemoryFlags() allows for memballoon
> (<currentMemory/>) changes for both active and inactive guests.
> And just before doing any change, we have to make sure that the
> new size is not greater than the total memory (<memory/>).
> 
> However, the total memory includes not only the regular guest
> memory, but also sum of maximum sizes of all virtio-mems (in fact
> all memory devices for that matter). But virtio-mem devices are
> modified differently (via virDomainUpdateDevice()) and thus the
> upper limit for new balloon size has to be lowered.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  src/qemu/qemu_driver.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index e376a64bee..6a9da62ded 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -2433,12 +2433,28 @@ static int qemuDomainSetMemoryFlags(virDomainPtr dom, unsigned long newmem,
>      } else {
>          /* resize the current memory */
>          unsigned long oldmax = 0;
> +        size_t i;
>  
> -        if (def)
> +        if (def) {
>              oldmax = virDomainDefGetMemoryTotal(def);
> +
> +            /* While virtio-mem is regular mem from guest POV, it can't be
> +             * modified through this API. */
> +            for (i = 0; i < def->nmems; i++) {
> +                if (def->mems[i]->model == VIR_DOMAIN_MEMORY_MODEL_VIRTIO_MEM)
> +                    oldmax -= def->mems[i]->size;
> +            }
> +        }
> +
>          if (persistentDef) {
> -            if (!oldmax || oldmax > virDomainDefGetMemoryTotal(persistentDef))
> +            if (!oldmax || oldmax > virDomainDefGetMemoryTotal(persistentDef)) {

IMO this code will not be correct any more when you do the subtraction
of virtio-mem devices above as you compare it with the total memory of
the persistent def.