[PATCH v1] KVM: arm64: selftests: Handle feature fields with nonzero minimum value correctly

[Jing Zhang]

Hi Suzuki,

On Mon, Jan 15, 2024 at 1:34 AM Suzuki K Poulose <suzuki.poulose at arm.com> wrote:
>
> On 09/01/2024 16:56, Jing Zhang wrote:
> > There are some feature fields with nonzero minimum valid value. Make
> > sure get_safe_value() won't return invalid field values for them.
> > Also fix a bug that wrongly uses the feature bits type as the feature
> > bits sign causing all fields as signed in the get_safe_value() and
> > get_invalid_value().
> >
> > Fixes: 54a9ea73527d ("KVM: arm64: selftests: Test for setting ID register from usersapce")
> > Reported-by: Zenghui Yu <yuzenghui at huawei.com>
> > Reported-by: Itaru Kitayama <itaru.kitayama at linux.dev>
> > Signed-off-by: Jing Zhang <jingzhangos at google.com>
> > ---
> >   .../selftests/kvm/aarch64/set_id_regs.c       | 20 +++++++++++++++----
> >   1 file changed, 16 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/testing/selftests/kvm/aarch64/set_id_regs.c b/tools/testing/selftests/kvm/aarch64/set_id_regs.c
> > index bac05210b539..f17454dc6d9e 100644
> > --- a/tools/testing/selftests/kvm/aarch64/set_id_regs.c
> > +++ b/tools/testing/selftests/kvm/aarch64/set_id_regs.c
> > @@ -224,13 +224,20 @@ uint64_t get_safe_value(const struct reg_ftr_bits *ftr_bits, uint64_t ftr)
> >   {
> >       uint64_t ftr_max = GENMASK_ULL(ARM64_FEATURE_FIELD_BITS - 1, 0);
> >
> > -     if (ftr_bits->type == FTR_UNSIGNED) {
> > +     if (ftr_bits->sign == FTR_UNSIGNED) {
> >               switch (ftr_bits->type) {
> >               case FTR_EXACT:
> >                       ftr = ftr_bits->safe_val;
> >                       break;
> >               case FTR_LOWER_SAFE:
> > -                     if (ftr > 0)
> > +                     uint64_t min_safe = 0;
> > +
> > +                     if (!strcmp(ftr_bits->name, "ID_AA64DFR0_EL1_DebugVer"))
> > +                             min_safe = ID_AA64DFR0_EL1_DebugVer_IMP;
> > +                     else if (!strcmp(ftr_bits->name, "ID_DFR0_EL1_CopDbg"))
> > +                             min_safe = ID_DFR0_EL1_CopDbg_Armv8;
>
> Instead of hardcoding the safe value here in the code, why not "fix" the
> safe value in the ftr_id table and use ftr_bits->safe_val for both the
> above cases ?
>

SGTM. Will do.
> > +
> > +                     if (ftr > min_safe)
> >                               ftr--;
> >                       break;
> >               case FTR_HIGHER_SAFE:
> > @@ -252,7 +259,12 @@ uint64_t get_safe_value(const struct reg_ftr_bits *ftr_bits, uint64_t ftr)
> >                       ftr = ftr_bits->safe_val;
> >                       break;
> >               case FTR_LOWER_SAFE:
> > -                     if (ftr > 0)
> > +                     uint64_t min_safe = 0;
> > +
> > +                     if (!strcmp(ftr_bits->name, "ID_DFR0_EL1_PerfMon"))
> > +                             min_safe = ID_DFR0_EL1_PerfMon_PMUv3;
> > +
> > +                     if (ftr > min_safe)
> >                               ftr--;
>
> Also, here, don't we need to type case both "ftr" and min_safe to
> int64_t for signed features ?

They are all used as unsigned on purpose. That's why the handling for
signed features are handled in different cases.
>
> Suzuki
>
> >                       break;
> >               case FTR_HIGHER_SAFE:
> > @@ -276,7 +288,7 @@ uint64_t get_invalid_value(const struct reg_ftr_bits *ftr_bits, uint64_t ftr)
> >   {
> >       uint64_t ftr_max = GENMASK_ULL(ARM64_FEATURE_FIELD_BITS - 1, 0);
> >
> > -     if (ftr_bits->type == FTR_UNSIGNED) {
> > +     if (ftr_bits->sign == FTR_UNSIGNED) {
> >               switch (ftr_bits->type) {
> >               case FTR_EXACT:
> >                       ftr = max((uint64_t)ftr_bits->safe_val + 1, ftr + 1);
> >
> > base-commit: 0dd3ee31125508cd67f7e7172247f05b7fd1753a
>

Thanks,
Jing