On Tue, 28 Dec 2021 09:26:22 +0000,
Andrew Jones <drjones@xxxxxxxxxx> wrote:
>
> On Mon, Dec 27, 2021 at 12:48:05PM +0000, Marc Zyngier wrote:
> > Contrary to popular belief, there is no such thing as a default
> > IPA size on arm64. Anything goes, and implementations are the
> > usual Wild West.
> >
> > The selftest infrastructure default to 40bit IPA, which obviously
> > doesn't work for some systems out there.
> >
> > Turn VM_MODE_DEFAULT from a constant into a variable, and let
> > guest_modes_append_default() populate it, depending on what
> > the HW can do. In order to preserve the current behaviour, we
> > still pick 40bits IPA as the default if it is available, and
> > the largest supported IPA space otherwise.
> >
> > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> > ---
> > .../testing/selftests/kvm/include/kvm_util.h | 4 ++-
> > tools/testing/selftests/kvm/lib/guest_modes.c | 30 +++++++++++++++++--
> > 2 files changed, 30 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> > index 2d62edc49d67..7fa0a93d7526 100644
> > --- a/tools/testing/selftests/kvm/include/kvm_util.h
> > +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> > @@ -53,7 +53,9 @@ enum vm_guest_mode {
> >
> > #if defined(__aarch64__)
> >
> > -#define VM_MODE_DEFAULT VM_MODE_P40V48_4K
> > +extern enum vm_guest_mode vm_mode_default;
> > +
> > +#define VM_MODE_DEFAULT vm_mode_default
> > #define MIN_PAGE_SHIFT 12U
> > #define ptes_per_page(page_size) ((page_size) / 8)
> >
> > diff --git a/tools/testing/selftests/kvm/lib/guest_modes.c b/tools/testing/selftests/kvm/lib/guest_modes.c
> > index c330f414ef96..5e3fdbd992fd 100644
> > --- a/tools/testing/selftests/kvm/lib/guest_modes.c
> > +++ b/tools/testing/selftests/kvm/lib/guest_modes.c
> > @@ -4,22 +4,46 @@
> > */
> > #include "guest_modes.h"
> >
> > +#ifdef __aarch64__
> > +enum vm_guest_mode vm_mode_default;
> > +#endif
> > +
> > struct guest_mode guest_modes[NUM_VM_MODES];
> >
> > void guest_modes_append_default(void)
> > {
> > +#ifndef __aarch64__
> > guest_mode_append(VM_MODE_DEFAULT, true, true);
> > -
> > -#ifdef __aarch64__
> > - guest_mode_append(VM_MODE_P40V48_64K, true, true);
> > +#else
> > {
> > unsigned int limit = kvm_check_cap(KVM_CAP_ARM_VM_IPA_SIZE);
> > + int i;
> > +
> > + vm_mode_default = NUM_VM_MODES;
> > +
> > if (limit >= 52)
> > guest_mode_append(VM_MODE_P52V48_64K, true, true);
> > if (limit >= 48) {
> > guest_mode_append(VM_MODE_P48V48_4K, true, true);
> > guest_mode_append(VM_MODE_P48V48_64K, true, true);
> > }
> > + if (limit >= 40) {
> > + guest_mode_append(VM_MODE_P40V48_4K, true, true);
> > + guest_mode_append(VM_MODE_P40V48_64K, true, true);
> > + vm_mode_default = VM_MODE_P40V48_4K;
> > + }
> > +
> > + /*
> > + * Pick the first supported IPA size if the default
> > + * isn't available.
> > + */
> > + for (i = 0; vm_mode_default == NUM_VM_MODES && i < NUM_VM_MODES; i++) {
> > + if (guest_modes[i].supported && guest_modes[i].enabled)
> > + vm_mode_default = i;
>
> Since we don't have a 'break' here, this picks the last supported size
> (of the guest_modes list), not the first, as the comment implies it should
> do.
This is checked in the for() loop condition, and the first matching
mode will cause the loop to terminate. This is the same check that
avoids scanning for a mode when VM_MODE_P40V48_4K is selected.
M.
--
Without deviation from the norm, progress is not possible.
