Re: [PATCH v4 10/10] KVM: selftests: Move memslot 0 above KVM internal memslots

Thomas Huth
2020-01-27T09:42:36Z

On 23/01/2020 19.04, Ben Gardon wrote:
> KVM creates internal memslots between 3 and 4 GiB paddrs on the first
> vCPU creation. If memslot 0 is large enough it collides with these
> memslots an causes vCPU creation to fail. Instead of creating memslot 0
> at paddr 0, start it 4G into the guest physical address space.
>
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
> tools/testing/selftests/kvm/lib/kvm_util.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 5b971c04f1643..427c88d32e988 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -130,9 +130,11 @@ _Static_assert(sizeof(vm_guest_mode_string)/sizeof(char *) == NUM_VM_MODES,
> *
> * Creates a VM with the mode specified by mode (e.g. VM_MODE_P52V48_4K).
> * When phy_pages is non-zero, a memory region of phy_pages physical pages
> - * is created and mapped starting at guest physical address 0. The file
> - * descriptor to control the created VM is created with the permissions
> - * given by perm (e.g. O_RDWR).
> + * is created, starting at 4G into the guest physical address space to avoid
> + * KVM internal memslots which map the region between 3G and 4G. If tests need
> + * to use the physical region between 0 and 3G, they can allocate another
> + * memslot for that region. The file descriptor to control the created VM is
> + * created with the permissions given by perm (e.g. O_RDWR).
> */
> struct kvm_vm *_vm_create(enum vm_guest_mode mode, uint64_t phy_pages, int perm)
> {
> @@ -231,7 +233,8 @@ struct kvm_vm *_vm_create(enum vm_guest_mode mode, uint64_t phy_pages, int perm)
> vm->vpages_mapped = sparsebit_alloc();
> if (phy_pages != 0)
> vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
> - 0, 0, phy_pages, 0);
> + KVM_INTERNAL_MEMSLOTS_END_PADDR,
> + 0, phy_pages, 0);
>
> return vm;
> }

This patch causes *all* tests on s390x to fail like this:

# selftests: kvm: sync_regs_test
# Testing guest mode: PA-bits:52, VA-bits:48, 4K pages
# ==== Test Assertion Failure ====
# lib/kvm_util.c:1059: false
# pid=248244 tid=248244 - Success
# 1 0x0000000001002f3d: addr_gpa2hva at kvm_util.c:1059
# 2 (inlined by) addr_gpa2hva at kvm_util.c:1047
# 3 0x0000000001006edf: addr_gva2gpa at processor.c:144
# 4 0x0000000001004345: addr_gva2hva at kvm_util.c:1636
# 5 0x00000000010077c1: kvm_vm_elf_load at elf.c:192
# 6 0x00000000010070c3: vm_create_default at processor.c:228
# 7 0x0000000001001347: main at sync_regs_test.c:87
# 8 0x000003ffba7a3461: ?? ??:0
# 9 0x0000000001001965: .annobin_init.c.hot at crt1.o:?
# 10 0xffffffffffffffff: ?? ??:0
# No vm physical memory at 0x0
not ok 2 selftests: kvm: sync_regs_test # exit=254

AFAIK the ELF binaries on s390x are linked to addresses below 4G, so
generally removing the memslot here seems to be a bad idea on s390x.

Thomas