Re: [PATCH v8 03/19] target/riscv/cpu.c: set satp_max_supported in cpu_riscv_set_satp()

[Andrew Jones]

On Thu, Nov 02, 2023 at 09:53:50AM -0300, Daniel Henrique Barboza wrote:
> 
> 
> On 11/2/23 06:24, Andrew Jones wrote:
> > On Wed, Nov 01, 2023 at 05:41:48PM -0300, Daniel Henrique Barboza wrote:
> > > The setter() for the boolean attributes that set satp_mode (sv32, sv39,
> > > sv48, sv57, sv64) considers that the CPU will always do a
> > > set_satp_mode_max_supported() during cpu_init().
> > > 
> > > This is not the case for the KVM 'host' CPU, and we'll add another CPU
> > > that won't set satp_mode_max() during cpu_init(). Users should be able
> > > to set a max_support in these circunstances.
> > > 
> > > Allow cpu_riscv_set_satp() to set satp_mode_max_supported if the CPU
> > > didn't set one prior.
> > > 
> > > Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> > > ---
> > >   target/riscv/cpu.c | 11 +++++++++++
> > >   1 file changed, 11 insertions(+)
> > > 
> > > diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> > > index 822970345c..9f6837ecb7 100644
> > > --- a/target/riscv/cpu.c
> > > +++ b/target/riscv/cpu.c
> > > @@ -1100,6 +1100,7 @@ static void cpu_riscv_get_satp(Object *obj, Visitor 
> > > *v, const char *name,
> > >   static void cpu_riscv_set_satp(Object *obj, Visitor *v, const char 
> > > *name,
> > >                                  void *opaque, Error **errp)
> > >   {
> > > +    RISCVCPU *cpu = RISCV_CPU(obj);
> > >       RISCVSATPMap *satp_map = opaque;
> > >       uint8_t satp = satp_mode_from_str(name);
> > >       bool value;
> > > @@ -1108,6 +1109,16 @@ static void cpu_riscv_set_satp(Object *obj, 
> > > Visitor *v, const char *name,
> > >           return;
> > >       }
> > > +    /*
> > > +     * Allow users to set satp max supported if the CPU didn't
> > > +     * set any during cpu_init(). First value set to 'true'
> > > +     * in this case is assumed to be the max supported for
> > > +     * the CPU.
> > 
> > Hmm, doesn't that mean if a user does
> > 
> >   -cpu rv64,sv39=true,sv48=true
> > 
> > then the max is set to sv39 instead of sv48?
> > 
> > I made a mistake in my last review by stating we shouldn't set the max
> > supported satp for rv64i to the maximum satp that TCG supports. I forgot
> > how all of it worked. Setting the _supported_ modes to the maximum that
> > TCG supports makes sense as long as we don't default to any of them for
> > rv64i. So, I think we should return the set_satp_mode_max_supported() to
> > rv64i's definition (passing VM_1_10_SV57 or maybe even VM_1_10_SV64) and
> > then change set_satp_mode_default_map() to error out for rv64i (or maybe
> > for all "bare" type cpus).
> 
> Ok, then let's set max supported mode to SV64 (the maximum we allow).
> 
> Then we don't need to do anything else - setting a max supported value will 
> allow
> TCG to handle it accordingly with OpenSBI and the kernel, and a suitable 
> satp_mode
> will be picked by them. We can leave finalize() untouched.
> 
> I'll make a note in cpu_init() to remind ourselves that we're not setting a 
> default
> satp_mode value, but a *limit* for the satp_mode value the CPU can handle.

It's both. It's the limit and, in the absence of user input, its used as
the default. Setting the limit is fine for a no-default cpu type, but
allowing it to become the default is not. We need to also modify
set_satp_mode_default_map() to only do what it does for non no-default
cpus types.

Thanks,
drew