Hello Andrew Jones,

The patch 14c47b7530e2: "kvm: selftests: introduce ucall" from Sep 18, 2018, leads to the following static checker warning:

./tools/testing/selftests/kvm/lib/ucall.c:61 ucall_init() warn: always true condition '(gpa >= 0) => (0-u64max >= 0)'

./tools/testing/selftests/kvm/lib/ucall.c 28 void ucall_init(struct kvm_vm *vm, ucall_type_t type, void *arg) 29 { 30 ucall_type = type; 31 sync_global_to_guest(vm, ucall_type); 32 33 if (type == UCALL_PIO) 34 return; 35 36 if (type == UCALL_MMIO) { 37 vm_paddr_t gpa, start, end, step;

vm_paddr_t is a u64.

38 bool ret; 39 40 if (arg) { 41 gpa = (vm_paddr_t)arg; 42 ret = ucall_mmio_init(vm, gpa); 43 TEST_ASSERT(ret, "Can't set ucall mmio address to %lx", gpa); 44 return; 45 } 46 47 /* 48 * Find an address within the allowed virtual address space, 49 * that does _not_ have a KVM memory region associated with it. 50 * Identity mapping an address like this allows the guest to 51 * access it, but as KVM doesn't know what to do with it, it 52 * will assume it's something userspace handles and exit with 53 * KVM_EXIT_MMIO. Well, at least that's how it works for AArch64. 54 * Here we start with a guess that the addresses around two 55 * thirds of the VA space are unmapped and then work both down 56 * and up from there in 1/6 VA space sized steps. 57 */ 58 start = 1ul << (vm->va_bits * 2 / 3); 59 end = 1ul << vm->va_bits; 60 step = 1ul << (vm->va_bits / 6); 61 for (gpa = start; gpa >= 0; gpa -= step) { ^^^^^^^^ So this doesn't work.

62 if (ucall_mmio_init(vm, gpa & ~(vm->page_size - 1))) 63 return; 64 } 65 for (gpa = start + step; gpa < end; gpa += step) { 66 if (ucall_mmio_init(vm, gpa & ~(vm->page_size - 1))) 67 return; 68 } 69 TEST_ASSERT(false, "Can't find a ucall mmio address"); 70 } 71 }

regards, dan carpenter