Re: [PATCH -fixes v3 1/2] riscv: Fix enabling cbo.zero when running in M-mode

[Alexandre Ghiti]

Hi Samuel,

On 14/02/2024 10:28, Andrew Jones wrote:
> On Wed, Feb 14, 2024 at 01:01:56AM -0800, Samuel Holland wrote:
> > When the kernel is running in M-mode, the CBZE bit must be set in the
> > menvcfg CSR, not in senvcfg.
> >
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Fixes: 43c16d51a19b ("RISC-V: Enable cbo.zero in usermode")
> > Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
> > ---
> >
> > (no changes since v1)
> >
> >   arch/riscv/include/asm/csr.h   | 2 ++
> >   arch/riscv/kernel/cpufeature.c | 2 +-
> >   2 files changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> > index 510014051f5d..2468c55933cd 100644
> > --- a/arch/riscv/include/asm/csr.h
> > +++ b/arch/riscv/include/asm/csr.h
> > @@ -424,6 +424,7 @@
> >   # define CSR_STATUS	CSR_MSTATUS
> >   # define CSR_IE		CSR_MIE
> >   # define CSR_TVEC	CSR_MTVEC
> > +# define CSR_ENVCFG	CSR_MENVCFG
> >   # define CSR_SCRATCH	CSR_MSCRATCH
> >   # define CSR_EPC	CSR_MEPC
> >   # define CSR_CAUSE	CSR_MCAUSE
> > @@ -448,6 +449,7 @@
> >   # define CSR_STATUS	CSR_SSTATUS
> >   # define CSR_IE		CSR_SIE
> >   # define CSR_TVEC	CSR_STVEC
> > +# define CSR_ENVCFG	CSR_SENVCFG
> >   # define CSR_SCRATCH	CSR_SSCRATCH
> >   # define CSR_EPC	CSR_SEPC
> >   # define CSR_CAUSE	CSR_SCAUSE
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index 89920f84d0a3..c5b13f7dd482 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -950,7 +950,7 @@ arch_initcall(check_unaligned_access_all_cpus);
> >   void riscv_user_isa_enable(void)
> >   {
> >   	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICBOZ))
> > -		csr_set(CSR_SENVCFG, ENVCFG_CBZE);
> > +		csr_set(CSR_ENVCFG, ENVCFG_CBZE);
> >   }
> >   
> >   #ifdef CONFIG_RISCV_ALTERNATIVE
> > --
> > 2.43.0
> After our back and forth on how we determine the existence of the *envcfg
> CSRs, I wonder if we shouldn't put a comment above this
> riscv_user_isa_enable() function capturing the [current] decision.
>
> Something like
>
>   /*
>    * While the [ms]envcfg CSRs weren't defined until priv spec 1.12,
>    * they're assumed to be present when an extension is present which
>    * specifies [ms]envcfg bit(s). Hence, we don't do any additional
>    * priv spec version checks or CSR probes here.
>    */


I was about to read the whole discussion in v2 to understand the 
v3...thank you Drew :) I think it really makes sense to add this 
comment, do you intend to do so Samuel?

Thanks,

Alex


> Thanks,
> drew
>
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