Re: [PATCH v2 1/2] KVM: arm64: Finalize guest-wide sysregs prior to per-vCPU sysregs

[sashiko-bot@kernel.org]

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

Pre-existing issues:
- [High] Numeric range comparison over sparse `enum vcpu_sysreg` covers unintended registers.
--

--- Patch [1]: [PATCH v2 1/2] KVM: arm64: Finalize guest-wide sysregs prior to per-vCPU sysregs ---
commit d51df44c26211dddcc71c5fe7798bb6cbbc7e67e
Author: Mark Brown <broonie@kernel.org>

KVM: arm64: Finalize guest-wide sysregs prior to per-vCPU sysregs

This commit splits the sysreg initialization into a per-VM and a per-vCPU
function to ensure that guest-wide settings are finalized before per-vCPU
NV initialization runs.

> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 5d5c579d45790..958d7ef78785f 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
[ ... ]
> @@ -5825,6 +5814,29 @@ int kvm_finalize_sys_regs(struct kvm_vcpu *vcpu)
[ ... ]
> +int kvm_vcpu_finalize_sys_regs(struct kvm_vcpu *vcpu)
> +{
[ ... ]
> +	if (vcpu_has_nv(vcpu)) {
> +		ret = kvm_init_nv_sysregs(vcpu);

[Severity: High]
This isn't a bug introduced by this patch, but does the initialization in
kvm_init_nv_sysregs() touch unintended registers by iterating over the
sparse vcpu_sysreg enumeration?

Looking at the loop at the end of kvm_init_nv_sysregs() in
arch/arm64/kvm/nested.c:

    for (enum vcpu_sysreg sr = __SANITISED_REG_START__; sr < NR_SYS_REGS; sr++)
        __vcpu_rmw_sys_reg(vcpu, sr, |=, 0);

Because VNCR-mapped entries are numbered by their VNCR-page byte offset
rather than declaration order, iterating using a numeric range comparison
over the enum covers unassigned gaps and other registers that happen to fall
in that byte span.

Could this loop inadvertently corrupt or desync guest state by treating
offsets as sequential enum entries?

> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260803-kvm-arm64-idreg-final-v2-0-d7d7e4efc640@kernel.org?part=1