linux-kernel - Re: [PATCH v7 11/21] RISC-V: KVM: Handle WFI exits for VCPU

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Date:   Mon, 23 Sep 2019 18:24:02 +0530
From:   Anup Patel <anup@...infault.org>
To:     Alexander Graf <graf@...zon.com>
Cc:     Anup Patel <Anup.Patel@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Paolo Bonzini <pbonzini@...hat.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: [PATCH v7 11/21] RISC-V: KVM: Handle WFI exits for VCPU

On Mon, Sep 23, 2019 at 12:24 PM Alexander Graf <graf@...zon.com> wrote:
>
>
>
> On 04.09.19 18:15, Anup Patel wrote:
> > We get illegal instruction trap whenever Guest/VM executes WFI
> > instruction.
> >
> > This patch handles WFI trap by blocking the trapped VCPU using
> > kvm_vcpu_block() API. The blocked VCPU will be automatically
> > resumed whenever a VCPU interrupt is injected from user-space
> > or from in-kernel IRQCHIP emulation.
> >
> > Signed-off-by: Anup Patel <anup.patel@....com>
> > Acked-by: Paolo Bonzini <pbonzini@...hat.com>
> > Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
> > ---
> >   arch/riscv/kvm/vcpu_exit.c | 72 ++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 72 insertions(+)
> >
> > diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
> > index d75a6c35b6c7..39469f67b241 100644
> > --- a/arch/riscv/kvm/vcpu_exit.c
> > +++ b/arch/riscv/kvm/vcpu_exit.c
> > @@ -12,6 +12,13 @@
> >   #include <linux/kvm_host.h>
> >   #include <asm/csr.h>
> >
> > +#define INSN_OPCODE_MASK     0x007c
> > +#define INSN_OPCODE_SHIFT    2
> > +#define INSN_OPCODE_SYSTEM   28
> > +
> > +#define INSN_MASK_WFI                0xffffff00
> > +#define INSN_MATCH_WFI               0x10500000
> > +
> >   #define INSN_MATCH_LB               0x3
> >   #define INSN_MASK_LB                0x707f
> >   #define INSN_MATCH_LH               0x1003
> > @@ -112,6 +119,67 @@
> >                                (s32)(((insn) >> 7) & 0x1f))
> >   #define MASK_FUNCT3         0x7000
> >
> > +static int truly_illegal_insn(struct kvm_vcpu *vcpu,
> > +                           struct kvm_run *run,
> > +                           ulong insn)
> > +{
> > +     /* Redirect trap to Guest VCPU */
> > +     kvm_riscv_vcpu_trap_redirect(vcpu, EXC_INST_ILLEGAL, insn);
> > +
> > +     return 1;
> > +}
> > +
> > +static int system_opcode_insn(struct kvm_vcpu *vcpu,
> > +                           struct kvm_run *run,
> > +                           ulong insn)
> > +{
> > +     if ((insn & INSN_MASK_WFI) == INSN_MATCH_WFI) {
> > +             vcpu->stat.wfi_exit_stat++;
> > +             if (!kvm_arch_vcpu_runnable(vcpu)) {
> > +                     srcu_read_unlock(&vcpu->kvm->srcu, vcpu->arch.srcu_idx);
> > +                     kvm_vcpu_block(vcpu);
> > +                     vcpu->arch.srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> > +                     kvm_clear_request(KVM_REQ_UNHALT, vcpu);
> > +             }
> > +             vcpu->arch.guest_context.sepc += INSN_LEN(insn);
> > +             return 1;
> > +     }
> > +
> > +     return truly_illegal_insn(vcpu, run, insn);
> > +}
> > +
> > +static int illegal_inst_fault(struct kvm_vcpu *vcpu, struct kvm_run *run,
> > +                           unsigned long insn)
> > +{
> > +     unsigned long ut_scause = 0;
> > +     struct kvm_cpu_context *ct;
> > +
> > +     if (unlikely((insn & 3) != 3)) {
>
> What do the low 2 bits mean here? Maybe you can use a define instead?

These bits are for instruction length (16bit or 32bit).

I will add appropriate defines for these bits.

Regards,
Anup

>
>
> Alex
>
>
>
>
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