Re: [PATCH] selftests: kvm: fix overlapping addresses in memslot_perf_test

[Paolo Bonzini]

On 28/05/21 21:51, Maciej S. Szmigiero wrote:
> On 28.05.2021 21:11, Paolo Bonzini wrote:
> > The memory that is allocated in vm_create is already mapped close to
> > GPA 0, because test_execute passes the requested memory to
> > prepare_vm.  This causes overlapping memory regions and the
> > test crashes.  For simplicity just move MEM_GPA higher.
> >
> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> I am not sure that I understand the issue correctly, is vm_create_default()
> already reserving low GPAs (around 0x10000000) on some arches or run
> environments?

It maps the number of pages you pass in the second argument, see
vm_create.

  if (phy_pages != 0)
    vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
                                0, 0, phy_pages, 0);

In this case:

  data->vm = vm_create_default(VCPU_ID, mempages, guest_code);

called here:

  if (!prepare_vm(data, nslots, maxslots, tdata->guest_code,
                  mem_size, slot_runtime)) {

where mempages is mem_size, which is declared as:

        uint64_t mem_size = tdata->mem_size ? : MEM_SIZE_PAGES;

but actually a better fix is just to pass a small fixed value (e.g. 
1024) to vm_create_default, since all other regions are added by hand.

Paolo