Re: [PATCH 1/3] target/arm: keep translation start level unsigned

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 31 Dec 2020 at 16:43, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 12/31/20 1:59 AM, Rémi Denis-Courmont wrote:
> > Le jeudi 31 décembre 2020, 00:38:14 EET Richard Henderson a écrit :
> >> On 12/30/20 2:10 PM, Richard Henderson wrote:
> >>> On 12/18/20 6:33 AM, remi.denis.courmont@huawei.com wrote:
> >>>> From: Rémi Denis-Courmont <remi.denis.courmont@huawei.com>
> >>>>
> >>>> Signed-off-by: Rémi Denis-Courmont <remi.denis.courmont@huawei.com>
> >>>> ---
> >>>>
> >>>>  target/arm/helper.c | 14 ++++++--------
> >>>>  1 file changed, 6 insertions(+), 8 deletions(-)
> >>>
> >>> The patch does more than what is described above.
> >>>
> >>>> diff --git a/target/arm/helper.c b/target/arm/helper.c
> >>>> index df195c314c..b927e53ab0 100644
> >>>> --- a/target/arm/helper.c
> >>>> +++ b/target/arm/helper.c
> >>>>
> >>>> @@ -10821,17 +10821,12 @@ do_fault:
> >>>>   * Returns true if the suggested S2 translation parameters are OK and
> >>>>   * false otherwise.
> >>>>   */
> >>>>
> >>>> -static bool check_s2_mmu_setup(ARMCPU *cpu, bool is_aa64, int level,
> >>>> +static bool check_s2_mmu_setup(ARMCPU *cpu, bool is_aa64, uint32_t
> >>>> level,
> >>>>
> >>>>                                 int inputsize, int stride)
> >>>>
> >>>>  {
> >>>>
> >>>>      const int grainsize = stride + 3;
> >>>>      int startsizecheck;
> >>>>
> >>>> -    /* Negative levels are never allowed.  */
> >>>> -    if (level < 0) {
> >>>> -        return false;
> >>>> -    }
> >>>> -
> >>>
> >>> I would expect this to be the only hunk from the patch description.
> >>> Probably changing this negative check to a >= 3 check.
> >>
> >> Having read the next patch, I think you should drop this type change.
> >>
> >>>> @@ -11203,7 +11201,7 @@ static bool get_phys_addr_lpae(CPUARMState *env,
> >>>> uint64_t address,>>
> >>>>          if (!aarch64 || stride == 9) {
> >>>>
> >>>>              /* AArch32 or 4KB pages */
> >>>>
> >>>> -            startlevel = 2 - sl0;
> >>>> +            startlevel = (2 - sl0) & 3;
> >>
> >> This hunk belongs with the next patch, implementing TTST, and should be
> >> conditional.  I.e.
> >>
> >>     if (stride == 9) {
> >>         startlevel = 2 - sl0;
> >>         if (aarch64 &&
> >>             cpu_isar_feature(aa64_st, env_archcpu(env)) {
> >>             startlevel &= 3;
> >>         }
> >
> > You can do that but:
> > 1) Nothing in the spec says that SL0 == b11 without ST means start level -1.
> > It's undefined, and I don't see any reasons to treat it differently than with
> > ST.
>
> By that logic there's no reason to treat it differently at all; you could drop
> the feature check entirely.  In lieu, -1 makes a decent error indicator.
>
> > 2) Functionally, checking for ST seems to belong naturally within
> > check_s2_mmu_setup() in this particular case.
>
> I guess.  I'll leave it to Peter's preference.

You've reviewed the patchset, I'm happy to go with whatever your
preference is (because I don't want to have to duplicate the
review work to form an opinion).

thanks
-- PMM