Re: [PATCH v4.5 09/36] KVM: s390: protvirt: Add initial vm and cpu lifecycle handling

Christian Borntraeger
2020-02-26T09:12:41Z

On 26.02.20 09:28, David Hildenbrand wrote:
> On 26.02.20 09:12, Christian Borntraeger wrote:
>>
>>
>> On 25.02.20 23:37, David Hildenbrand wrote:
>>>
>>>> +static int kvm_s390_pv_alloc_vm(struct kvm *kvm)
>>>> +{
>>>> + unsigned long base = uv_info.guest_base_stor_len;
>>>> + unsigned long virt = uv_info.guest_virt_var_stor_len;
>>>> + unsigned long npages = 0, vlen = 0;
>>>> + struct kvm_memory_slot *memslot;
>>>> +
>>>> + kvm->arch.pv.stor_var = NULL;
>>>> + kvm->arch.pv.stor_base = __get_free_pages(GFP_KERNEL, get_order(base));
>>>> + if (!kvm->arch.pv.stor_base)
>>>> + return -ENOMEM;
>>>> +
>>>> + /*
>>>> + * Calculate current guest storage for allocation of the
>>>> + * variable storage, which is based on the length in MB.
>>>> + *
>>>> + * Slots are sorted by GFN
>>>> + */
>>>> + mutex_lock(&kvm->slots_lock);
>>>> + memslot = kvm_memslots(kvm)->memslots;
>>>> + npages = memslot->base_gfn + memslot->npages;
>>>> + mutex_unlock(&kvm->slots_lock);
>>>
>>> As discussed, I think we should just use mem_limit and check against
>>> some hardcoded upper limit. But yeah, we can do that as an addon (in
>>> which case memory hotplug will require special tweaks to detect this
>>> from user space ... e.g., a new capability)
>>>
>>>
>>> [...]
>>>
>>>> +int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
>>>> +{
>>>> + struct uv_cb_cgc uvcb = {
>>>> + .header.cmd = UVC_CMD_CREATE_SEC_CONF,
>>>> + .header.len = sizeof(uvcb)
>>>> + };
>>>> + int cc, ret;
>>>> + u16 dummy;
>>>> +
>>>> + ret = kvm_s390_pv_alloc_vm(kvm);
>>>> + if (ret)
>>>> + return ret;
>>>> +
>>>> + /* Inputs */
>>>> + uvcb.guest_stor_origin = 0; /* MSO is 0 for KVM */
>>>> + uvcb.guest_stor_len = kvm->arch.pv.guest_len;
>>>> + uvcb.guest_asce = kvm->arch.gmap->asce;
>>>> + uvcb.guest_sca = (unsigned long)kvm->arch.sca;
>>>> + uvcb.conf_base_stor_origin = (u64)kvm->arch.pv.stor_base;
>>>> + uvcb.conf_virt_stor_origin = (u64)kvm->arch.pv.stor_var;
>>>> +
>>>> + cc = uv_call(0, (u64)&uvcb);
>>>> + *rc = uvcb.header.rc;
>>>> + *rrc = uvcb.header.rrc;
>>>> + KVM_UV_EVENT(kvm, 3, "PROTVIRT CREATE VM: handle %llx len %llx rc %x rrc %x",
>>>> + uvcb.guest_handle, uvcb.guest_stor_len, *rc, *rrc);
>>>> +
>>>> + /* Outputs */
>>>> + kvm->arch.pv.handle = uvcb.guest_handle;
>>>> +
>>>> + if (cc) {
>>>> + if (uvcb.header.rc & UVC_RC_NEED_DESTROY)
>>>> + kvm_s390_pv_deinit_vm(kvm, &dummy, &dummy);
>>>> + else
>>>> + kvm_s390_pv_dealloc_vm(kvm);
>>>> + return -EIO;
>>>
>>> A lot easier to read :)
>>>
>>>
>>> Fell free add my rb with or without the mem_limit change.
>>
>> I think I will keep the memslot logic. For hotplug we actually need
>> to notify the ultravisor that the guest size has changed as only the
>> ultravisor will be able to inject an addressing exception.
>
> So holes in between memory slots won't be properly considered? What will
> happen if a guest accesses such memory right now?

QEMU would get a fault (just like when QEMU would read from a non-existing mapping).
I think this is ok, as for non-secure this would also trigger a crash (in the guest
though) since we do not provide the proper memory increment handling in QEMU after
we have dropped the standby memory support.

>> Lets keep it simple for now
>>
>
> I double checked (virt/kvm/kvm_main.c:update_memslots()), and the slots
> are definitely sorted "based on their GFN". I think, it's lowest GFN
> first, so the code in here would be wrong with more than one slot.
>
> Can you double check, because I might misinterpret the code.

kvm_s390_get_cmma also uses the first memslot to calculate the buffer size.
I verified that with a hacked QEMU and printk that this is indeed sorted
started with the last memslot.