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

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Date:   Tue, 30 Jul 2019 18:21:24 +0530
From:   Anup Patel <anup@...infault.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Anup Patel <Anup.Patel@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Radim K <rkrcmar@...hat.com>,
        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>,
        "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 Tue, Jul 30, 2019 at 3:04 PM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> 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.

This is a good suggestion. I will use kvm_arch_hardware_enable() for
programming HIDELEG and HEDELEG CSRs.

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

They don't matter in HS-mode so we don't need to access them in
vcpu_switch.S

Regards,
Anup