linux-kernel - Re: [PATCH v20 16/30] LoongArch: KVM: Implement update VM id function

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Date:   Mon, 11 Sep 2023 18:00:19 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Tianrui Zhao <zhaotianrui@...ngson.cn>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        WANG Xuerui <kernel@...0n.name>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        loongarch@...ts.linux.dev, Jens Axboe <axboe@...nel.dk>,
        Mark Brown <broonie@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        Oliver Upton <oliver.upton@...ux.dev>, maobibo@...ngson.cn,
        Xi Ruoyao <xry111@...111.site>
Subject: Re: [PATCH v20 16/30] LoongArch: KVM: Implement update VM id function

Hi, Tianrui,

On Thu, Aug 31, 2023 at 4:30 PM Tianrui Zhao <zhaotianrui@...ngson.cn> wrote:
>
> Implement kvm check vmid and update vmid, the vmid should be checked before
> vcpu enter guest.
>
> Reviewed-by: Bibo Mao <maobibo@...ngson.cn>
> Signed-off-by: Tianrui Zhao <zhaotianrui@...ngson.cn>
> ---
>  arch/loongarch/kvm/vmid.c | 66 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 66 insertions(+)
>  create mode 100644 arch/loongarch/kvm/vmid.c
>
> diff --git a/arch/loongarch/kvm/vmid.c b/arch/loongarch/kvm/vmid.c
> new file mode 100644
> index 0000000000..fc25ddc3b7
> --- /dev/null
> +++ b/arch/loongarch/kvm/vmid.c
> @@ -0,0 +1,66 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2020-2023 Loongson Technology Corporation Limited
> + */
> +
> +#include <linux/kvm_host.h>
> +#include "trace.h"
> +
> +static void _kvm_update_vpid(struct kvm_vcpu *vcpu, int cpu)
> +{
> +       struct kvm_context *context;
> +       unsigned long vpid;
> +
> +       context = per_cpu_ptr(vcpu->kvm->arch.vmcs, cpu);
> +       vpid = context->vpid_cache + 1;
> +       if (!(vpid & vpid_mask)) {
> +               /* finish round of 64 bit loop */
> +               if (unlikely(!vpid))
> +                       vpid = vpid_mask + 1;
> +
> +               /* vpid 0 reserved for root */
> +               ++vpid;
> +
> +               /* start new vpid cycle */
> +               kvm_flush_tlb_all();
> +       }
> +
> +       context->vpid_cache = vpid;
> +       vcpu->arch.vpid = vpid;
> +}
> +
> +void _kvm_check_vmid(struct kvm_vcpu *vcpu)
> +{
> +       struct kvm_context *context;
> +       bool migrated;
> +       unsigned long ver, old, vpid;
> +       int cpu;
> +
> +       cpu = smp_processor_id();
> +       /*
> +        * Are we entering guest context on a different CPU to last time?
> +        * If so, the vCPU's guest TLB state on this CPU may be stale.
> +        */
> +       context = per_cpu_ptr(vcpu->kvm->arch.vmcs, cpu);
> +       migrated = (vcpu->cpu != cpu);
> +
> +       /*
> +        * Check if our vpid is of an older version
> +        *
> +        * We also discard the stored vpid if we've executed on
> +        * another CPU, as the guest mappings may have changed without
> +        * hypervisor knowledge.
> +        */
> +       ver = vcpu->arch.vpid & ~vpid_mask;
> +       old = context->vpid_cache  & ~vpid_mask;
> +       if (migrated || (ver != old)) {
> +               _kvm_update_vpid(vcpu, cpu);
> +               trace_kvm_vpid_change(vcpu, vcpu->arch.vpid);
> +               vcpu->cpu = cpu;
> +       }
> +
> +       /* Restore GSTAT(0x50).vpid */
> +       vpid = (vcpu->arch.vpid & vpid_mask)
> +               << CSR_GSTAT_GID_SHIFT;
> +       change_csr_gstat(vpid_mask << CSR_GSTAT_GID_SHIFT, vpid);
> +}
I believe that vpid and vmid are both GID in the gstat register, so
please unify their names. And I think vpid is better than vmid.

Moreover, no need to create a vmid.c file, just putting them in main.c is OK.

Huacai

> --
> 2.27.0
>