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

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Message-ID: <3c149ec4-38df-9073-2880-b28148d3c059@amazon.com>
Date:   Mon, 23 Sep 2019 08:53:49 +0200
From:   Alexander Graf <graf@...zon.com>
To:     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>
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: [PATCH v7 11/21] RISC-V: KVM: Handle WFI exits for VCPU



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?


Alex




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