Re: [PATCH v3 2/4] RISC-V: KVM: Add SBI FWFT validation support

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] The FWFT SBI extension defaults to enabled, breaking live migration and violating KVM ABI guidelines.
--

--- Patch [2]: [PATCH v3 2/4] RISC-V: KVM: Add SBI FWFT validation support ---
commit 9a4432f98b4fe06897baf4b85a503109a0f2b7f8
Author: Inochi Amaoto <inochiama@gmail.com>

RISC-V: KVM: Add SBI FWFT validation support

This commit implements extension parameters validation support for the KVM
SBI FWFT extension.

> diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
> index 1342adb3180c6..2794e9e5b495e 100644
> --- a/arch/riscv/kvm/vcpu_sbi_fwft.c
> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c

[ ... ]

> @@ -574,6 +598,7 @@ const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft = {
>  	.init = kvm_sbi_ext_fwft_init,
>  	.deinit = kvm_sbi_ext_fwft_deinit,
>  	.reset = kvm_sbi_ext_fwft_reset,
> +	.validate = kvm_sbi_ext_fwft_validate,
[Severity: High]
This isn't a bug introduced by this patch, but does this extension default
to enabled because it lacks the .default_disabled = true flag in this
struct?

If an older userspace creates a VM on a new kernel with the FWFT extension,
the kernel silently exposes this capability to the guest. If the guest uses
this feature and is subsequently live-migrated to an older kernel that
lacks FWFT support, will the migration silently fail when the extension
unexpectedly disappears?

Could we add .default_disabled = true to vcpu_sbi_ext_fwft to ensure proper
capability negotiation?

>  	.state_reg_subtype = KVM_REG_RISCV_SBI_FWFT,
>  	.get_state_reg_count = kvm_sbi_ext_fwft_get_reg_count,
>  	.get_state_reg_id = kvm_sbi_ext_fwft_get_reg_id,

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260729232527.139183-1-inochiama@gmail.com?part=2