Re: [PATCH v3] KVM: selftests: riscv: Add lazy V extension enablement for guests

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The replacement of `guest_unexp_trap` with the full exception vector table silently removes guest register dumps (`vcpu_dump()`) on unexpected exceptions, significantly degrading debuggability.
--

--- Patch [1]: [PATCH v3] KVM: selftests: riscv: Add lazy V extension enablement for guests ---
commit f9473f3696d28b72282cabd505ada7d8de6f8b19
Author: jinrui <jinrui@haiwei.tech>

KVM: selftests: riscv: Add lazy V extension enablement for guests

This commit adds lazy V extension enablement for guests to handle compiler
auto-vectorization on hosts with V extension. It replaces the unused
guest_unexp_trap() handler with the full exception vector table, allowing
safe lazy enablement in route_exception().

> diff --git a/tools/testing/selftests/kvm/lib/riscv/processor.c b/tools/testing/selftests/kvm/lib/riscv/processor.c
> index ded5429f34483..841474acfabd1 100644
> --- a/tools/testing/selftests/kvm/lib/riscv/processor.c
> +++ b/tools/testing/selftests/kvm/lib/riscv/processor.c
> @@ -297,14 +297,6 @@ void vcpu_arch_dump(FILE *stream, struct kvm_vcpu *vcpu, u8 indent)
>  		" T3: 0x%016lx   T4: 0x%016lx T5: 0x%016lx T6: 0x%016lx\n",
>  		core.regs.t3, core.regs.t4, core.regs.t5, core.regs.t6);
>  }
> -
> -static void __aligned(16) guest_unexp_trap(void)
> -{
> -	sbi_ecall(KVM_RISCV_SELFTESTS_SBI_EXT,
> -		  KVM_RISCV_SELFTESTS_SBI_UNEXP,
> -		  0, 0, 0, 0, 0, 0);
> -}
> -

[Severity: Medium]
Does removing guest_unexp_trap() result in the loss of guest register dumps
on unexpected exceptions?

This deleted function triggered KVM_RISCV_SELFTESTS_SBI_UNEXP, which
explicitly yielded a vcpu_dump() on the host side. With the new default
exception handler calling kvm_exit_unexpected_exception() instead, it maps
to UCALL_UNHANDLED.

On the host side, assert_on_unhandled_exception() catches this but lacks
the vcpu_dump() call:

tools/testing/selftests/kvm/lib/riscv/processor.c:assert_on_unhandled_exception() {
	struct ucall uc;

	if (get_ucall(vcpu, &uc) == UCALL_UNHANDLED) {
		TEST_FAIL("Unexpected exception (vector:0x%lx, ec:0x%lx)",
			uc.args[0], uc.args[1]);
	}
}

Will this make it harder to debug guest test failures due to missing PC and
register states?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/574AACF6F4298057+20260721112454.330498-1-jinrui@haiwei.tech?part=1