Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [RFC PATCH v2 07/19] RISC-V: KVM: Implement
 KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls
To:     Anup Patel <Anup.Patel@wdc.com>,
        Palmer Dabbelt <palmer@sifive.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Radim K <rkrcmar@redhat.com>
Cc:     Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Atish Patra <Atish.Patra@wdc.com>,
        Alistair Francis <Alistair.Francis@wdc.com>,
        Damien Le Moal <Damien.LeMoal@wdc.com>,
        Christoph Hellwig <hch@infradead.org>,
        Anup Patel <anup@brainfault.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20190802074620.115029-1-anup.patel@wdc.com>
 <20190802074620.115029-8-anup.patel@wdc.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Openpgp: preference=signencrypt
Message-ID: <03f60f3a-bb50-9210-8352-da16cca322b9@redhat.com>
Date:   Fri, 2 Aug 2019 11:03:45 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <20190802074620.115029-8-anup.patel@wdc.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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