Messages in this thread |  | | From | "Maciej S. Szmigiero" <> | Subject | Re: [PATCH] selftests: kvm: fix overlapping addresses in memslot_perf_test | Date | Sun, 30 May 2021 01:13:36 +0200 |
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On 29.05.2021 12:20, Paolo Bonzini wrote: > 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@redhat.com> >> >> 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
Yes, but the argument that is passed to vm_create_default() (mem_size in the case of the test) is not passed as phy_pages to vm_create(). Rather, vm_create_with_vcpus() calculates some upper bound of extra memory that is needed to cover that much guest memory (including for its page tables).
The biggest possible mem_size from memslot_perf_test is 512 MiB + 1 page, according to my calculations this results in phy_pages of 1029 (~4 MiB) in the x86-64 case and around 1540 (~6 MiB) in the s390x case (here I am not sure about the exact number, since s390x has some additional alignment requirements).
Both values are well below 256 MiB (0x10000000UL), so I was wondering what kind of circumstances can make these allocations collide (maybe I am missing something in my analysis).
> > Paolo >
Thanks, Maciej
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