Re: [RFC PATCH v2 07/19] RISC-V: KVM: Implement KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls

[Paolo Bonzini]

On 02/08/19 09:47, Anup Patel wrote:
> +     if (reg_num == KVM_REG_RISCV_CSR_REG(sip))
> +             kvm_riscv_vcpu_flush_interrupts(vcpu, false);

Not updating the vsip CSR here can cause an interrupt to be lost, if the
next call to kvm_riscv_vcpu_flush_interrupts finds a zero mask.

You could add a new field vcpu->vsip_shadow that is updated every time
CSR_VSIP is written (including kvm_arch_vcpu_load) with a function like

void kvm_riscv_update_vsip(struct kvm_vcpu *vcpu)
{
        if (vcpu->vsip_shadow != vcpu->arch.guest_csr.vsip) {
                csr_write(CSR_VSIP, vcpu->arch.guest_csr.vsip);
                vcpu->vsip_shadow = vcpu->arch.guest_csr.vsip;
        }
}

And just call this unconditionally from kvm_vcpu_ioctl_run.  The cost is
just a memory load per VS-mode entry, it should hardly be measurable.

Paolo