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Date: Wed, 8 May 2024 17:07:30 -0700
From: Charlie Jenkins <charlie@rivosinc.com>
To: Andy Chiu <andy.chiu@sifive.com>
Cc: Deepak Gupta <debug@rivosinc.com>, paul.walmsley@sifive.com,
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Subject: Re: [PATCH v3 05/29] riscv: zicfiss / zicfilp enumeration
Message-ID: <ZjwTwvaYSFAuB1qr@ghost>
References: <20240403234054.2020347-1-debug@rivosinc.com>
 <20240403234054.2020347-6-debug@rivosinc.com>
 <CABgGipX3vXeJ_RKnV17pE-NH6=L0XUF2sdKea7hZHbuq4skh_A@mail.gmail.com>
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On Thu, May 09, 2024 at 08:00:00AM +0800, Andy Chiu wrote:
> Hi Deepak,
> 
> On Thu, Apr 4, 2024 at 7:41 AM Deepak Gupta <debug@rivosinc.com> wrote:
> >
> > This patch adds support for detecting zicfiss and zicfilp. zicfiss and
> > zicfilp stands for unprivleged integer spec extension for shadow stack
> > and branch tracking on indirect branches, respectively.
> >
> > This patch looks for zicfiss and zicfilp in device tree and accordinlgy
> > lights up bit in cpu feature bitmap. Furthermore this patch adds detection
> > utility functions to return whether shadow stack or landing pads are
> > supported by cpu.
> >
> > Signed-off-by: Deepak Gupta <debug@rivosinc.com>
> > ---
> >  arch/riscv/include/asm/cpufeature.h | 13 +++++++++++++
> >  arch/riscv/include/asm/hwcap.h      |  2 ++
> >  arch/riscv/include/asm/processor.h  |  1 +
> >  arch/riscv/kernel/cpufeature.c      |  2 ++
> >  4 files changed, 18 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> > index 0bd11862b760..f0fb8d8ae273 100644
> > --- a/arch/riscv/include/asm/cpufeature.h
> > +++ b/arch/riscv/include/asm/cpufeature.h
> > @@ -8,6 +8,7 @@
> >
> >  #include <linux/bitmap.h>
> >  #include <linux/jump_label.h>
> > +#include <linux/smp.h>
> >  #include <asm/hwcap.h>
> >  #include <asm/alternative-macros.h>
> >  #include <asm/errno.h>
> > @@ -137,4 +138,16 @@ static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsi
> >
> >  DECLARE_STATIC_KEY_FALSE(fast_misaligned_access_speed_key);
> >
> > +static inline bool cpu_supports_shadow_stack(void)
> > +{
> > +       return (IS_ENABLED(CONFIG_RISCV_USER_CFI) &&
> > +                   riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICFISS));
> > +}
> > +
> > +static inline bool cpu_supports_indirect_br_lp_instr(void)
> > +{
> > +       return (IS_ENABLED(CONFIG_RISCV_USER_CFI) &&
> > +                   riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICFILP));
> > +}
> > +
> >  #endif
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index 1f2d2599c655..74b6c727f545 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -80,6 +80,8 @@
> >  #define RISCV_ISA_EXT_ZFA              71
> >  #define RISCV_ISA_EXT_ZTSO             72
> >  #define RISCV_ISA_EXT_ZACAS            73
> nit: two tabs for alignment
> 

Deepak, I think you might be using tabs with a display size of 4 spaces
that causes a couple of places to have incorrect alignment but would
look correct with 4 spaces. Linux uses 8 spaces for tabs.

- Charlie

> 
> > +#define RISCV_ISA_EXT_ZICFILP  74
> > +#define RISCV_ISA_EXT_ZICFISS  75
> >
> >  #define RISCV_ISA_EXT_XLINUXENVCFG     127
> >
> > diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> > index a8509cc31ab2..6c5b3d928b12 100644
> > --- a/arch/riscv/include/asm/processor.h
> > +++ b/arch/riscv/include/asm/processor.h
> > @@ -13,6 +13,7 @@
> >  #include <vdso/processor.h>
> >
> >  #include <asm/ptrace.h>
> > +#include <asm/hwcap.h>
> >
> >  #ifdef CONFIG_64BIT
> >  #define DEFAULT_MAP_WINDOW     (UL(1) << (MMAP_VA_BITS - 1))
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index 79a5a35fab96..d052cad5b82f 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -263,6 +263,8 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
> >         __RISCV_ISA_EXT_DATA(h, RISCV_ISA_EXT_h),
> >         __RISCV_ISA_EXT_SUPERSET(zicbom, RISCV_ISA_EXT_ZICBOM, riscv_xlinuxenvcfg_exts),
> >         __RISCV_ISA_EXT_SUPERSET(zicboz, RISCV_ISA_EXT_ZICBOZ, riscv_xlinuxenvcfg_exts),
> > +       __RISCV_ISA_EXT_SUPERSET(zicfilp, RISCV_ISA_EXT_ZICFILP, riscv_xlinuxenvcfg_exts),
> > +       __RISCV_ISA_EXT_SUPERSET(zicfiss, RISCV_ISA_EXT_ZICFISS, riscv_xlinuxenvcfg_exts),
> >         __RISCV_ISA_EXT_DATA(zicntr, RISCV_ISA_EXT_ZICNTR),
> >         __RISCV_ISA_EXT_DATA(zicond, RISCV_ISA_EXT_ZICOND),
> >         __RISCV_ISA_EXT_DATA(zicsr, RISCV_ISA_EXT_ZICSR),
> > --
> > 2.43.2
> >
> 
> Thanks,
> Andy