On Thu, Nov 11, 2021, Ben Gardon wrote:
> On Wed, Nov 10, 2021 at 4:03 PM David Matlack <dmatlack@xxxxxxxxxx> wrote:
> >
> > From: Sean Christopherson <seanjc@xxxxxxxxxx>
> >
> > Assert that the GPA for a memslot backed by a hugepage is aligned to
> > the hugepage size and fix perf_test_util accordingly. Lack of GPA
> > alignment prevents KVM from backing the guest with hugepages, e.g. x86's
> > write-protection of hugepages when dirty logging is activated is
> > otherwise not exercised.
> >
> > Add a comment explaining that guest_page_size is for non-huge pages to
> > try and avoid confusion about what it actually tracks.
> >
> > Cc: Ben Gardon <bgardon@xxxxxxxxxx>
> > Cc: Yanan Wang <wangyanan55@xxxxxxxxxx>
> > Cc: Andrew Jones <drjones@xxxxxxxxxx>
> > Cc: Peter Xu <peterx@xxxxxxxxxx>
> > Cc: Aaron Lewis <aaronlewis@xxxxxxxxxx>
> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > [Used get_backing_src_pagesz() to determine alignment dynamically.]
> > Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
> > ---
> > tools/testing/selftests/kvm/lib/kvm_util.c | 2 ++
> > tools/testing/selftests/kvm/lib/perf_test_util.c | 7 ++++++-
> > 2 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> > index 07f37456bba0..1f6a01c33dce 100644
> > --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> > @@ -875,6 +875,8 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
> > if (src_type == VM_MEM_SRC_ANONYMOUS_THP)
> > alignment = max(backing_src_pagesz, alignment);
> >
> > + ASSERT_EQ(guest_paddr, align_up(guest_paddr, backing_src_pagesz));
> > +
> > /* Add enough memory to align up if necessary */
> > if (alignment > 1)
> > region->mmap_size += alignment;
> > diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c
> > index 6b8d5020dc54..a015f267d945 100644
> > --- a/tools/testing/selftests/kvm/lib/perf_test_util.c
> > +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
> > @@ -55,11 +55,16 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus,
> > {
> > struct kvm_vm *vm;
> > uint64_t guest_num_pages;
> > + uint64_t backing_src_pagesz = get_backing_src_pagesz(backing_src);
> > int i;
> >
> > pr_info("Testing guest mode: %s\n", vm_guest_mode_string(mode));
> >
> > perf_test_args.host_page_size = getpagesize();
> > + /*
> > + * Snapshot the non-huge page size. This is used by the guest code to
> > + * access/dirty pages at the logging granularity.
> > + */
> > perf_test_args.guest_page_size = vm_guest_mode_params[mode].page_size;
>
> Is this comment correct? I wouldn't expect the guest page size to
> determine the host dirty logging granularity.
"guest page size" is a bit of a misnomer. It's not the page size of the guest's
page tables, rather it's the non-huge page size of the PTEs that KVM uses to map
guest memory. That info is exposed to the guest so that the guest and host agree
on the stride.
> > guest_num_pages = vm_adjust_num_guest_pages(mode,
> > @@ -92,7 +97,7 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus,
> >
> > guest_test_phys_mem = (vm_get_max_gfn(vm) - guest_num_pages) *
> > perf_test_args.guest_page_size;
> > - guest_test_phys_mem = align_down(guest_test_phys_mem, perf_test_args.host_page_size);
> > + guest_test_phys_mem = align_down(guest_test_phys_mem, backing_src_pagesz);
> > #ifdef __s390x__
> > /* Align to 1M (segment size) */
> > guest_test_phys_mem = align_down(guest_test_phys_mem, 1 << 20);
> > --
> > 2.34.0.rc1.387.gb447b232ab-goog
> >
