Re: [PATCH 2/3] RISC-V: hwprobe: Expose Zbc and the scalar crypto extensions

From: Samuel Ortiz
Date: Mon Jul 10 2023 - 03:59:50 EST

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On Wed, Jun 28, 2023 at 09:25:02AM -0400, Stefan O'Rear wrote:
> On Wed, Jun 28, 2023, at 6:04 AM, Samuel Ortiz wrote:
> > On Tue, Jun 27, 2023 at 08:34:20PM -0400, Stefan O'Rear wrote:
> >> On Tue, Jun 27, 2023, at 10:37 AM, Samuel Ortiz wrote:
> >> > Zbc was missing from a previous Bit-Manipulation extension hwprobe
> >> > patch.
> >> >
> >> > Add all scalar crypto extensions bits, and define a macro for setting
> >> > the hwprobe key/pair in a more readable way.
> >> >
> >> > Signed-off-by: Samuel Ortiz <sameo@xxxxxxxxxxxx>
> >> > ---
> >> > Documentation/riscv/hwprobe.rst | 33 ++++++++++++++++++++++++
> >> > arch/riscv/include/uapi/asm/hwprobe.h | 11 ++++++++
> >> > arch/riscv/kernel/sys_riscv.c | 36 ++++++++++++++++-----------
> >> > 3 files changed, 66 insertions(+), 14 deletions(-)
> >> >
> >> > diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
> >> > index 19165ebd82ba..3177550106e0 100644
> >> > --- a/Documentation/riscv/hwprobe.rst
> >> > +++ b/Documentation/riscv/hwprobe.rst
> >> > @@ -72,11 +72,44 @@ The following keys are defined:
> >> > extensions.
> >> >
> >> > * :c:macro:`RISCV_HWPROBE_EXT_ZBB`: The Zbb extension is supported,
> >> > as defined
> >> > + in version 1.0 of the Bit-Manipulation ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZBC`: The Zbc extension is supported,
> >> > as defined
> >> > in version 1.0 of the Bit-Manipulation ISA extensions.
> >> >
> >> > * :c:macro:`RISCV_HWPROBE_EXT_ZBS`: The Zbs extension is supported,
> >> > as defined
> >> > in version 1.0 of the Bit-Manipulation ISA extensions.
> >> >
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZBKB`: The Zbkb extension is
> >> > supported, as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZBKC`: The Zbkc extension is
> >> > supported, as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZBKX`: The Zbkx extension is
> >> > supported, as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZKND`: The Zknd extension is
> >> > supported, as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZKNE`: The Zkne extension is
> >> > supported, as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZKNH`: The Zknh extension is
> >> > supported, as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZKR`: The Zkr extension is supported,
> >> > as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZKSED`: The Zksed extension is
> >> > supported, as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZKSH`: The Zksh extension is
> >> > supported, as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > + * :c:macro:`RISCV_HWPROBE_EXT_ZKT`: The Zkt extension is supported,
> >> > as defined
> >> > + in version 1.0 of the Scalar Cryptography ISA extensions.
> >> > +
> >> > * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains
> >> > performance
> >> > information about the selected set of processors.
> >> >
> >> > diff --git a/arch/riscv/include/uapi/asm/hwprobe.h
> >> > b/arch/riscv/include/uapi/asm/hwprobe.h
> >> > index 006bfb48343d..8357052061b3 100644
> >> > --- a/arch/riscv/include/uapi/asm/hwprobe.h
> >> > +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> >> > @@ -29,6 +29,17 @@ struct riscv_hwprobe {
> >> > #define RISCV_HWPROBE_EXT_ZBA (1 << 3)
> >> > #define RISCV_HWPROBE_EXT_ZBB (1 << 4)
> >> > #define RISCV_HWPROBE_EXT_ZBS (1 << 5)
> >> > +#define RISCV_HWPROBE_EXT_ZBC (1 << 6)
> >> > +#define RISCV_HWPROBE_EXT_ZBKB (1 << 7)
> >> > +#define RISCV_HWPROBE_EXT_ZBKC (1 << 8)
> >> > +#define RISCV_HWPROBE_EXT_ZBKX (1 << 9)
> >> > +#define RISCV_HWPROBE_EXT_ZKND (1 << 10)
> >> > +#define RISCV_HWPROBE_EXT_ZKNE (1 << 11)
> >> > +#define RISCV_HWPROBE_EXT_ZKNH (1 << 12)
> >> > +#define RISCV_HWPROBE_EXT_ZKR (1 << 13)
> >> > +#define RISCV_HWPROBE_EXT_ZKSED (1 << 14)
> >> > +#define RISCV_HWPROBE_EXT_ZKSH (1 << 15)
> >> > +#define RISCV_HWPROBE_EXT_ZKT (1 << 16)
> >> > #define RISCV_HWPROBE_KEY_CPUPERF_0 5
> >> > #define RISCV_HWPROBE_MISALIGNED_UNKNOWN (0 << 0)
> >> > #define RISCV_HWPROBE_MISALIGNED_EMULATED (1 << 0)
> >> > diff --git a/arch/riscv/kernel/sys_riscv.c
> >> > b/arch/riscv/kernel/sys_riscv.c
> >> > index 26ef5526bfb4..df15926196b6 100644
> >> > --- a/arch/riscv/kernel/sys_riscv.c
> >> > +++ b/arch/riscv/kernel/sys_riscv.c
> >> > @@ -145,20 +145,28 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe
> >> > *pair,
> >> > for_each_cpu(cpu, cpus) {
> >> > struct riscv_isainfo *isainfo = &hart_isa[cpu];
> >> >
> >> > - if (riscv_isa_extension_available(isainfo->isa, ZBA))
> >> > - pair->value |= RISCV_HWPROBE_EXT_ZBA;
> >> > - else
> >> > - missing |= RISCV_HWPROBE_EXT_ZBA;
> >> > -
> >> > - if (riscv_isa_extension_available(isainfo->isa, ZBB))
> >> > - pair->value |= RISCV_HWPROBE_EXT_ZBB;
> >> > - else
> >> > - missing |= RISCV_HWPROBE_EXT_ZBB;
> >> > -
> >> > - if (riscv_isa_extension_available(isainfo->isa, ZBS))
> >> > - pair->value |= RISCV_HWPROBE_EXT_ZBS;
> >> > - else
> >> > - missing |= RISCV_HWPROBE_EXT_ZBS;
> >> > +#define SET_HWPROBE_EXT_PAIR(ext) \
> >> > + do { \
> >> > + if (riscv_isa_extension_available(isainfo->isa, ext)) \
> >> > + pair->value |= RISCV_HWPROBE_EXT_## ext; \
> >> > + else \
> >> > + missing |= RISCV_HWPROBE_EXT_## ext; \
> >> > + } while (false) \
> >> > +
> >> > + SET_HWPROBE_EXT_PAIR(ZBA);
> >> > + SET_HWPROBE_EXT_PAIR(ZBB);
> >> > + SET_HWPROBE_EXT_PAIR(ZBC);
> >> > + SET_HWPROBE_EXT_PAIR(ZBS);
> >> > + SET_HWPROBE_EXT_PAIR(ZBKB);
> >> > + SET_HWPROBE_EXT_PAIR(ZBKC);
> >> > + SET_HWPROBE_EXT_PAIR(ZBKX);
> >> > + SET_HWPROBE_EXT_PAIR(ZKND);
> >> > + SET_HWPROBE_EXT_PAIR(ZKNE);
> >> > + SET_HWPROBE_EXT_PAIR(ZKNH);
> >> > + SET_HWPROBE_EXT_PAIR(ZKR);
> >>
> >> Does the presence of a HWPROBE_EXT bit imply that userspace software can
> >> actually directly use the described feature? If so, we should probably
> >> not set ZKR unless mseccfg.USEED=1.
> >
> > mseccfg is MRW, so only accessible from M-mode only afaiu. So I don't
> > think we would be able to check that from Linux in S-mode.
>
> Check directly, no, but your patch already makes the assumption that
> mseccfg.SSEED=1 if zkr is present in the device tree. Which is fine as long
> as that contract is documented somewhere (presumably, the device tree
> binding; some of the language in the RVA22U64 profile spec implies USEED=0,
> but linux does not require profiles and they don't exist for rv32).
>
> If we want U-mode behavior to be discoverable and/or predictable, we have
> three good options:

Thanks for the suggestions.

> Simplest: Document that we expect USEED=0 or USEED=1. Set zkr appropriately
> in hwprobe.
>
> Most flexible: Work with the SBI people to add a SBI_EXT_FWFEATURE for USEED,
> as well as defining the value on kernel entry. Expose this via hwprobe and
> a new prctl.

I'd like to go down that route, but this depends on [1] to get
accepted/merged first.

Would it make sense to go with only documenting the USEED expectation
for now and then move to the more flexible FWFEATURE SBI approach?

Cheers,
Samuel.

[1] https://lists.riscv.org/g/tech-prs/message/540

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