[PATCH v5 07/17] riscv: Add B to hwcap and hwprobe

[Guodong Xu]

On Wed, 01 Jul 2026 13:27:54 +0000, sashiko-bot at kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The new B base extension is added to the host's hwcap and hwprobe, but KVM support was omitted, preventing VMMs from enabling it for guests.
> --
>
> commit 1f4cf004cf603a91f99c0c6776c5ca74728ca05e
> Author: Andrew Jones <andrew.jones at oss.qualcomm.com>
>
> riscv: Add B to hwcap and hwprobe
>
> Add B to hwcap and ensure when B is present that Zba, Zbb, and Zbs
> are all set. Also expose B via hwprobe so that userspace can probe B directly.
>
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index 0acb7a01ecc0f..58523b3a1998a 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -11,6 +11,7 @@
> >  #include <uapi/asm/hwcap.h>
> >
> >  #define RISCV_ISA_EXT_A		('a' - 'a')
> > +#define RISCV_ISA_EXT_B		('b' - 'a')
>
> [Severity: Medium]
> Since the B extension is now exposed to the host, does this patch also need
> to add KVM support so VMMs can pass the B extension to guests?
>
> Without adding KVM_RISCV_ISA_EXT_B to enum KVM_RISCV_ISA_EXT_ID in
> arch/riscv/include/uapi/asm/kvm.h and the corresponding KVM_ISA_EXT_ARR(B)
> mapping in arch/riscv/kvm/isa.c, KVM's ONE_REG handler will drop the
> configuration request.
>
> When a VMM configures a guest's ISA by writing to KVM_REG_RISCV_CONFIG_REG(isa)
> with the B bit set, kvm_riscv_base2isa_ext() will return KVM_RISCV_ISA_EXT_MAX
> and explicitly clear the bit from the requested register value.

I will send another series to expose extensions to KVM guests.
Let's settle the current series first.

Guodong