Re: [PATCH v6 3/5] riscv: Allow user to set the satp mode

[Alexandre Ghiti]

On Mon, Jan 23, 2023 at 11:14 AM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> On Mon, Jan 23, 2023 at 10:03:22AM +0100, Alexandre Ghiti wrote:
> > RISC-V specifies multiple sizes for addressable memory and Linux probes for
> > the machine's support at startup via the satp CSR register (done in
> > csr.c:validate_vm).
> >
> > As per the specification, sv64 must support sv57, which in turn must
> > support sv48...etc. So we can restrict machine support by simply setting the
> > "highest" supported mode and the bare mode is always supported.
> >
> > You can set the satp mode using the new properties "sv32", "sv39", "sv48",
> > "sv57" and "sv64" as follows:
> > -cpu rv64,sv57=on  # Linux will boot using sv57 scheme
> > -cpu rv64,sv39=on  # Linux will boot using sv39 scheme
> > -cpu rv64,sv57=off # Linux will boot using sv48 scheme
> > -cpu rv64          # Linux will boot using sv57 scheme by default
> >
> > We take the highest level set by the user:
> > -cpu rv64,sv48=on,sv57=on # Linux will boot using sv57 scheme
> >
> > We make sure that invalid configurations are rejected:
> > -cpu rv64,sv32=on # Can't enable 32-bit satp mode in 64-bit
> > -cpu rv64,sv39=off,sv48=on # sv39 must be supported if higher modes are
> >                            # enabled
> >
> > We accept "redundant" configurations:
> > -cpu rv64,sv48=on,sv57=off # Linux will boot using sv48 scheme
> >
> > And contradictory configurations:
> > -cpu rv64,sv48=on,sv48=off # Linux will boot using sv39 scheme
> >
> > In addition, we now correctly set the device-tree entry 'mmu-type' using
> > those new properties.
>
> This sentence no longer applies to this patch.


Sorry about that and thanks for noticing.

Alex

>
> Thanks,
> drew