linux-kernel - Re: [PATCH v4 00/11] KVM: VMX: Clean up Hyper-V PV TLB flush

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Message-ID: <f1edcb01-41f5-d26f-e8d6-0dbd09a1eb89@redhat.com>
Date:   Mon, 8 Mar 2021 12:50:26 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH v4 00/11] KVM: VMX: Clean up Hyper-V PV TLB flush

On 05/03/21 19:31, Sean Christopherson wrote:
> Clean up KVM's PV TLB flushing when running with EPT on Hyper-V, i.e. as
> a nested VMM.  No real goal in mind other than the sole patch in v1, which
> is a minor change to avoid a future mixup when TDX also wants to define
> .remote_flush_tlb.  Everything else is opportunistic clean up.
> 
> NOTE: Based on my NPT+SME bug fix series[*] due to multiple conflicts with
>        non-trivial resolutions.
> 
> [*] https://lkml.kernel.org/r/20210305011101.3597423-1-seanjc@google.com
> 
> 
> Patch 1 legitimately tested on VMX and SVM (including i386).  Patches 2+
> smoke tested by hacking usage of the relevant flows without actually
> routing to the Hyper-V hypercalls (partial hack-a-patch below).
> 
> -static inline int hv_remote_flush_root_ept(hpa_t root_ept,
> +static inline int hv_remote_flush_root_ept(struct kvm *kvm, hpa_t root_ept,
>                                             struct kvm_tlb_range *range)
>   {
> -       if (range)
> -               return hyperv_flush_guest_mapping_range(root_ept,
> -                               kvm_fill_hv_flush_list_func, (void *)range);
> -       else
> -               return hyperv_flush_guest_mapping(root_ept);
> +       if (range) {
> +               kvm_make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH);
> +               return 0;
> +       }
> +
> +       return -ENOMEM;
>   }
>   
>   static int hv_remote_flush_tlb_with_range(struct kvm *kvm,
> @@ -7753,8 +7754,7 @@ static __init int hardware_setup(void)
>                  vmx_x86_ops.update_cr8_intercept = NULL;
>   
>   #if IS_ENABLED(CONFIG_HYPERV)
> -       if (ms_hyperv.nested_features & HV_X64_NESTED_GUEST_MAPPING_FLUSH
> -           && enable_ept) {
> +       if (enable_ept) {
>                  vmx_x86_ops.tlb_remote_flush = hv_remote_flush_tlb;
>                  vmx_x86_ops.tlb_remote_flush_with_range =
>                                  hv_remote_flush_tlb_with_range;
> 
> v4:
>    - Rebased to kvm/queue, commit fe5f0041c026 ("KVM/SVM: Move vmenter.S
>      exception fixups out of line"), plus the aforementioned series.
>    - Don't grab PCID for nested_cr3 (NPT). [Paolo]
>    - Collect reviews. [Vitaly]
> 
> v3:
>    - https://lkml.kernel.org/r/20201027212346.23409-1-sean.j.christopherson@intel.com
>    - Add a patch to pass the root_hpa instead of pgd to vmx_load_mmu_pgd()
>      and retrieve the active PCID only when necessary.  [Vitaly]
>    - Selectively collects reviews (skipped a few due to changes). [Vitaly]
>    - Explicitly invalidate hv_tlb_eptp instead of leaving it valid when
>      the mismatch tracker "knows" it's invalid. [Vitaly]
>    - Change the last patch to use "hv_root_ept" instead of "hv_tlb_pgd"
>      to better reflect what is actually being tracked.
> 
> v2:
>    - Rewrite everything.
>    - https://lkml.kernel.org/r/20201020215613.8972-1-sean.j.christopherson@intel.com
> 
> v1: ???
> 
> Sean Christopherson (11):
>    KVM: x86: Get active PCID only when writing a CR3 value
>    KVM: VMX: Track common EPTP for Hyper-V's paravirt TLB flush
>    KVM: VMX: Stash kvm_vmx in a local variable for Hyper-V paravirt TLB
>      flush
>    KVM: VMX: Fold Hyper-V EPTP checking into it's only caller
>    KVM: VMX: Do Hyper-V TLB flush iff vCPU's EPTP hasn't been flushed
>    KVM: VMX: Invalidate hv_tlb_eptp to denote an EPTP mismatch
>    KVM: VMX: Don't invalidate hv_tlb_eptp if the new EPTP matches
>    KVM: VMX: Explicitly check for hv_remote_flush_tlb when loading pgd
>    KVM: VMX: Define Hyper-V paravirt TLB flush fields iff Hyper-V is
>      enabled
>    KVM: VMX: Skip additional Hyper-V TLB EPTP flushes if one fails
>    KVM: VMX: Track root HPA instead of EPTP for paravirt Hyper-V TLB
>      flush
> 
>   arch/x86/include/asm/kvm_host.h |   4 +-
>   arch/x86/kvm/mmu.h              |   4 +-
>   arch/x86/kvm/svm/svm.c          |  10 ++-
>   arch/x86/kvm/vmx/vmx.c          | 134 ++++++++++++++++++--------------
>   arch/x86/kvm/vmx/vmx.h          |  19 ++---
>   5 files changed, 92 insertions(+), 79 deletions(-)
> 

Huh, I was sure I had queued this already for 5.12.  Well, done so now.

Paolo