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

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Date:   Tue, 12 Sep 2023 11:51:58 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     bibo mao <maobibo@...ngson.cn>
Cc:     Tianrui Zhao <zhaotianrui@...ngson.cn>,
        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>,
        Xi Ruoyao <xry111@...111.site>
Subject: Re: [PATCH v20 16/30] LoongArch: KVM: Implement update VM id function

On Mon, Sep 11, 2023 at 6:23 PM bibo mao <maobibo@...ngson.cn> wrote:
>
>
>
> 在 2023/9/11 18:00, Huacai Chen 写道:
> > 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.
>
> For processor 3A5000 vpid is the same with vmid, with next generation processor
> like 3A6000, it is seperated. vpid is for vcpu specific and represents
> translation from gva to gpa; vmid is the whole vm and represents translation
> from gpa to hpa, all vcpus shares the same vmid, so that tlb indexed with vpid
> will be still in effective when flushing shadow tlbs indexed with vmid.
>
> Only that VM patch for 3A6000 is not submitted now, generation method for
> vpid and vmid will be much different. It is prepared for future processor
> update :)
If so, then I think there should be a 'vmid' in kvm_arch and a 'vpid'
in kvm_vcpu_arch?
This patch only handles kvm_vcpu_arch so I think all should be vpid here.

And again, this code can be just put in main.c.

Huacai

>
> Regards
> Bibo Mao
>
> >
> > Moreover, no need to create a vmid.c file, just putting them in main.c is OK.
> >
> > Huacai
> >
> >> --
> >> 2.27.0
> >>
>