[PATCH RFC v4 0/3] riscv: add Svukte extension

[Max Hsu]

RISC-V privileged spec will be added with Svukte extension [1] 

Svukte introduce senvcfg.UKTE and hstatus.HUKTE bitfield.
which makes user-mode access to supervisor memory raise page faults
in constant time, mitigating attacks that attempt to discover the 
supervisor software's address-space layout.

In the Linux kernel, since the hstatus.HU bit is not enabled,
the following patches only enable the use of senvcfg.UKTE.

For Guest environments, because a Guest OS (not limited to Linux)
may hold mappings from GVA to GPA, the Guest OS should decide
whether to enable the protection provided by the Svukte extension.

Since the Guest OS may utilize the Svukte extension simply by setting
the senvcfg.UKTE without any trap to host. In the view of VMM, the
Svukte extension should be always presented. Therefore adding an
extra entry in kvm_riscv_vcpu_isa_disable_allowed().

If the Guest environment wants to change senvcfg.UKTE, KVM already
provides the senvcfg CSR swap support via 
kvm_riscv_vcpu_swap_in_(host|guest)_state.
Thus, there is no concern about the Guest OS affecting the Host OS. 

The following patches add 
- dt-binding of Svukte ISA string
- CSR bit definition, ISA detection, senvcfg.UKTE enablement in kernel
- KVM ISA support for Svukte extension

Changes in v4:
- rebase on riscv/for-next
- add kvm_riscv_vcpu_isa_disable_allowed() entry addressed by Anup
  and Andrew from v2/v3 patches.
  - update the cover letter for the detailed reason
- update the commit message on dt-binding for the Svukte ISA string
- Link to v3: https://lore.kernel.org/all/20241120-dev-maxh-svukte-v3-v3-0-1e533d41ae15@sifive.com/

Changes in v3: 
- rebase on riscv/for-next
- fixed typo in the dt-binding for the Svukte ISA string
- updated the commit message for KVM support for the Svukte extension
- Link to v2: https://lore.kernel.org/all/20240927-dev-maxh-svukte-rebase-2-v2-0-9afe57c33aee@sifive.com/

Changes in v2: 
- rebase on riscv/for-next (riscv-for-linus-6.12-mw1)
- modify the description of dt-binding on Svukte ISA string
- Link to v1: https://lore.kernel.org/all/20240920-dev-maxh-svukte-rebase-v1-0-7864a88a62bd@sifive.com/

Link: https://github.com/riscv/riscv-isa-manual/pull/1564 [1] 

Signed-off-by: Max Hsu <max.hsu at sifive.com>

---
Max Hsu (3):
      dt-bindings: riscv: Add Svukte entry
      riscv: Add Svukte extension support
      riscv: KVM: Add Svukte extension support for Guest/VM

 Documentation/devicetree/bindings/riscv/extensions.yaml | 9 +++++++++
 arch/riscv/include/asm/csr.h                            | 2 ++
 arch/riscv/include/asm/hwcap.h                          | 1 +
 arch/riscv/include/uapi/asm/kvm.h                       | 1 +
 arch/riscv/kernel/cpufeature.c                          | 5 +++++
 arch/riscv/kvm/vcpu_onereg.c                            | 2 ++
 6 files changed, 20 insertions(+)
---
base-commit: fac04efc5c793dccbd07e2d59af9f90b7fc0dca4
change-id: 20241213-dev-maxh-svukte-v4-34101ec945e9

Best regards,
-- 
Max Hsu <max.hsu at sifive.com>