Re: [PATCH v2] KVM: selftests: Fix 32-bit truncation of vm_get_max_gfn()

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On 08.06.21 10:39, Christian Borntraeger wrote:


On 21.05.21 19:38, David Matlack wrote:
vm_get_max_gfn() casts vm->max_gfn from a uint64_t to an unsigned int,
which causes the upper 32-bits of the max_gfn to get truncated.

Nobody noticed until now likely because vm_get_max_gfn() is only used
as a mechanism to create a memslot in an unused region of the guest
physical address space (the top), and the top of the 32-bit physical
address space was always good enough.

This fix reveals a bug in memslot_modification_stress_test which was
trying to create a dummy memslot past the end of guest physical memory.
Fix that by moving the dummy memslot lower.

Fixes: 52200d0d944e ("KVM: selftests: Remove duplicate guest mode handling")
Reviewed-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxxxx>
Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>

As a heads up:
I have not yet looked into this, but this broke demand_paging_test and kvm_page_table_test
on s390:

not ok 4 selftests: kvm: demand_paging_test # exit=254
# selftests: kvm: dirty_log_test
# ==== Test Assertion Failure ====
#   lib/kvm_util.c:900: ret == 0
#   pid=245410 tid=245410 errno=22 - Invalid argument
#      1    0x0000000001005457: vm_userspace_mem_region_add at kvm_util.c:900
#      2    0x0000000001002cbf: run_test at dirty_log_test.c:757
#      3     (inlined by) run_test at dirty_log_test.c:702
#      4    0x000000000100c055: for_each_guest_mode at guest_modes.c:37
#      5    0x00000000010022b5: main at dirty_log_test.c:929 (discriminator 3)
#      6    0x000003ff96fabdb3: ?? ??:0
#      7    0x000000000100241d: .annobin_lto.hot at crt1.o:?
#   KVM_SET_USER_MEMORY_REGION IOCTL failed,
#   rc: -1 errno: 22
#   slot: 1 flags: 0x1
#   guest_phys_addr: 0xfffffbfe00000 size: 0x40100000

Ah. We do have a limit of 128TB for guest physical memory. The patch now made this
apparent as we no longer cut the upper bits off.



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