Subject: Re: [PATCH v13 25/35] KVM: selftests: Convert lib's mem regions to KVM_SET_USER_MEMORY_REGION2

From: Sean Christopherson <[email-masked]>
Date: Thu, 25 Apr 2024 08:09:49 -0700

On Thu, Apr 25, 2024, Shuah Khan wrote:
> On 4/25/24 08:12, Dan Carpenter wrote:
> > On Fri, Oct 27, 2023 at 11:22:07AM -0700, Sean Christopherson wrote:
> > > Use KVM_SET_USER_MEMORY_REGION2 throughout KVM's selftests library so that
> > > support for guest private memory can be added without needing an entirely
> > > separate set of helpers.
> > > 
> > > Note, this obviously makes selftests backwards-incompatible with older KVM
> >    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > versions from this point forward.
> >    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > 
> > Is there a way we could disable the tests on older kernels instead of
> > making them fail?  Check uname or something?  There is probably a
> > standard way to do this...  It's these tests which fail.
> 
> They shouldn't fail - the tests should be skipped on older kernels.

Ah, that makes sense.  Except for a few outliers that aren't all that interesting,
all KVM selftests create memslots, so I'm tempted to just make it a hard requirement
to spare us headache, e.g.

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index b2262b5fad9e..4b2038b1f11f 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -2306,6 +2306,9 @@ void __attribute((constructor)) kvm_selftest_init(void)
        /* Tell stdout not to buffer its content. */
        setbuf(stdout, NULL);
 
+       __TEST_REQUIRE(kvm_has_cap(KVM_CAP_USER_MEMORY2),
+                      "KVM selftests from v6.8+ require KVM_SET_USER_MEMORY_REGION2");
+
        kvm_selftest_arch_init();
 }

--

but it's also easy enough to be more precise and skip only those that actually
create memslots.

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index b2262b5fad9e..b21152adf448 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -944,6 +944,9 @@ int __vm_set_user_memory_region2(struct kvm_vm *vm, uint32_t slot, uint32_t flag
                .guest_memfd_offset = guest_memfd_offset,
        };
 
+       __TEST_REQUIRE(kvm_has_cap(KVM_CAP_USER_MEMORY2),
+                      "KVM selftests from v6.8+ require KVM_SET_USER_MEMORY_REGION2");
+
        return ioctl(vm->fd, KVM_SET_USER_MEMORY_REGION2, &region);
 }
 
@@ -970,6 +973,9 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
        size_t mem_size = npages * vm->page_size;
        size_t alignment;
 
+       __TEST_REQUIRE(kvm_has_cap(KVM_CAP_USER_MEMORY2),
+                      "KVM selftests from v6.8+ require KVM_SET_USER_MEMORY_REGION2");
+
        TEST_ASSERT(vm_adjust_num_guest_pages(vm->mode, npages) == npages,
                "Number of guest pages is not compatible with the host. "
                "Try npages=%d", vm_adjust_num_guest_pages(vm->mode, npages));
--