Re: [PATCH] KVM: selftests: fix steal_time for arm64 with host page size > 4K

[Sean Christopherson <seanjc@google.com>]

On Mon, Jun 29, 2026, Sebastian Ott wrote:
> On Sun, 28 Jun 2026, Zenghui Yu wrote:
> 
> > On 6/22/26 10:14 PM, Sebastian Ott wrote:
> > > 
> > > Fix the following failure when running with 16K host page size:
> > > ==== Test Assertion Failure ====
> > >   lib/kvm_util.c:991: vm_adjust_num_guest_pages(vm->mode, npages) == npages
> > >   pid=873 tid=873 errno=0 - Success
> > >      1  0x0000000000405a27: vm_mem_add at kvm_util.c:991
> > >      2  0x000000000040241f: check_steal_time_uapi at steal_time.c:223 (discriminator 7)
> > >      3   (inlined by) main at steal_time.c:539 (discriminator 7)
> > >      4  0x00007fff8b57af3b: ?? ??:0
> > >      5  0x00007fff8b57b007: ?? ??:0
> > >      6  0x0000000000402b6f: _start at ??:?
> > >   Number of guest pages is not compatible with the host. Try npages=4
> > > 
> > > Fixes: fc240715fc50 ("KVM: selftests: arm64: Fix steal_time test after UAPI refactoring")
> > > Reported-by: Zenghui Yu <zenghui.yu@linux.dev>
> > > Link: https://lore.kernel.org/kvmarm/7575a845-a542-4b16-b512-aec3126f97f3@linux.dev/T/#u
> > > Signed-off-by: Sebastian Ott <sebott@redhat.com>
> > > ---
> > >  tools/testing/selftests/kvm/steal_time.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/tools/testing/selftests/kvm/steal_time.c b/tools/testing/selftests/kvm/steal_time.c
> > > index 76fcdd1fd3cb..cdb81f3ee4b2 100644
> > > --- a/tools/testing/selftests/kvm/steal_time.c
> > > +++ b/tools/testing/selftests/kvm/steal_time.c
> > > @@ -208,6 +208,7 @@ static void check_steal_time_uapi(void)
> > >  {
> > >      struct kvm_vm *vm;
> > >      struct kvm_vcpu *vcpu;
> > > +    unsigned int gpages;
> > >      u64 st_ipa;
> > >      int ret;
> > > 
> > > @@ -220,8 +221,9 @@ static void check_steal_time_uapi(void)
> > >      };
> > > 
> > >      vcpu_ioctl(vcpu, KVM_HAS_DEVICE_ATTR, &dev);
> > > -    vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, ST_GPA_BASE, 1, 1, 0);
> > > -    virt_map(vm, ST_GPA_BASE, ST_GPA_BASE, 1);
> > > +    gpages = vm_calc_num_guest_pages(VM_MODE_DEFAULT, 1);
> > 
> > Would vm_calc_num_guest_pages(VM_MODE_DEFAULT, STEAL_TIME_SIZE) be better
> > to describe the number of pages we want to add?
> 
> Hm, I don't think we care. This is just for the uapi checker - the vm/vcpu
> doesn't even run..

Even though we don't truly care, we can "fix" that and dedup code at the same
time.  E.g.

diff --git a/tools/testing/selftests/kvm/steal_time.c b/tools/testing/selftests/kvm/steal_time.c
index bc3c62b72c58..c0256d4c4b09 100644
--- a/tools/testing/selftests/kvm/steal_time.c
+++ b/tools/testing/selftests/kvm/steal_time.c
@@ -27,6 +27,9 @@
 static void *st_gva[NR_VCPUS];
 static u64 guest_stolen_time[NR_VCPUS];
 
+static struct kvm_vm *vm_create_steal_time(u32 nr_vcpus, void *guest_code,
+                                          struct kvm_vcpu *vcpus[]);
+
 #if defined(__x86_64__)
 
 /* steal_time must have 64-byte alignment */
@@ -210,17 +213,14 @@ static void check_steal_time_uapi(void)
        u64 st_ipa;
        int ret;
 
-       vm = vm_create_with_one_vcpu(&vcpu, NULL);
-
        struct kvm_device_attr dev = {
                .group = KVM_ARM_VCPU_PVTIME_CTRL,
                .attr = KVM_ARM_VCPU_PVTIME_IPA,
                .addr = (u64)&st_ipa,
        };
 
+       vm = vm_create_steal_time(1, NULL, &vcpu);
        vcpu_ioctl(vcpu, KVM_HAS_DEVICE_ATTR, &dev);
-       vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, ST_GPA_BASE, 1, 1, 0);
-       virt_map(vm, ST_GPA_BASE, ST_GPA_BASE, 1);
 
        st_ipa = (ulong)ST_GPA_BASE | 1;
        ret = __vcpu_ioctl(vcpu, KVM_SET_DEVICE_ATTR, &dev);
@@ -500,13 +500,26 @@ static void run_vcpu(struct kvm_vcpu *vcpu)
        }
 }
 
+static struct kvm_vm *vm_create_steal_time(u32 nr_vcpus, void *guest_code,
+                                          struct kvm_vcpu *vcpus[])
+{
+       unsigned int gpages;
+       struct kvm_vm *vm;
+
+       vm = vm_create_with_vcpus(NR_VCPUS, guest_code, vcpus);
+       gpages = vm_calc_num_guest_pages(VM_MODE_DEFAULT, STEAL_TIME_SIZE * nr_vcpus);
+       vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, ST_GPA_BASE, 1, gpages, 0);
+       virt_map(vm, ST_GPA_BASE, ST_GPA_BASE, gpages);
+
+       return vm;
+}
+
 int main(int ac, char **av)
 {
        struct kvm_vcpu *vcpus[NR_VCPUS];
        struct kvm_vm *vm;
        pthread_t thread;
        cpu_set_t cpuset;
-       unsigned int gpages;
        long stolen_time;
        long run_delay;
        bool verbose;
@@ -518,10 +531,7 @@ int main(int ac, char **av)
        cpu = pin_self_to_any_cpu();
 
        /* Create a VM and an identity mapped memslot for the steal time structure */
-       vm = vm_create_with_vcpus(NR_VCPUS, guest_code, vcpus);
-       gpages = vm_calc_num_guest_pages(VM_MODE_DEFAULT, STEAL_TIME_SIZE * NR_VCPUS);
-       vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, ST_GPA_BASE, 1, gpages, 0);
-       virt_map(vm, ST_GPA_BASE, ST_GPA_BASE, gpages);
+       vm = vm_create_steal_time(NR_VCPUS, guest_code, vcpus);
 
        ksft_print_header();
        TEST_REQUIRE(is_steal_time_supported(vcpus[0]));