linux-kernel - Re: [RFC PATCH 07/16] RISC-V: KVM: Implement VCPU world-switch

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Date:   Tue, 30 Jul 2019 11:34:28 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Anup Patel <Anup.Patel@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Radim K <rkrcmar@...hat.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Anup Patel <anup@...infault.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 07/16] RISC-V: KVM: Implement VCPU world-switch

On 29/07/19 13:57, Anup Patel wrote:
>  void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>  {
> -	/* TODO: */
> +	struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
> +
> +	csr_write(CSR_HIDELEG, csr->hideleg);
> +	csr_write(CSR_HEDELEG, csr->hedeleg);

Writing HIDELEG and HEDELEG here seems either wrong or inefficient to me.

I don't remember the spec well enough, but there are two cases:

1) either they only matter while the guest runs and then you can set
them in kvm_arch_hardware_enable.  KVM common code takes care of doing
this on all CPUs for you.

2) or they also matter while the host runs and then you need to set them
in vcpu_switch.S.

Paolo