linux-kernel - Re: [PATCH 12/16] KVM: TDX: Inhibit APICv for TDX guest

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Message-ID: <CAGtprH9UBZe64zay0HjZRg5f--xM85Yt+jYijKZw=sfxRH=2Ow@mail.gmail.com>
Date: Fri, 3 Jan 2025 13:59:52 -0800
From: Vishal Annapurve <vannapurve@...gle.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: pbonzini@...hat.com, seanjc@...gle.com, kvm@...r.kernel.org, 
	rick.p.edgecombe@...el.com, kai.huang@...el.com, adrian.hunter@...el.com, 
	reinette.chatre@...el.com, xiaoyao.li@...el.com, 
	tony.lindgren@...ux.intel.com, isaku.yamahata@...el.com, yan.y.zhao@...el.com, 
	chao.gao@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/16] KVM: TDX: Inhibit APICv for TDX guest

On Sun, Dec 8, 2024 at 5:11 PM Binbin Wu <binbin.wu@...ux.intel.com> wrote:
>
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> Inhibit APICv for TDX guest in KVM since TDX doesn't support APICv accesses
> from host VMM.
>
> Follow how SEV inhibits APICv.  I.e, define a new inhibit reason for TDX, set
> it on TD initialization, and add the flag to kvm_x86_ops.required_apicv_inhibits.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
> ---
> TDX interrupts breakout:
> - Removed WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm)) in
>   tdx_td_vcpu_init(). (Rick)
> - Change APICV -> APICv in changelog for consistency.
> - Split the changelog to 2 paragraphs.
> ---
>  arch/x86/include/asm/kvm_host.h | 12 +++++++++++-
>  arch/x86/kvm/vmx/main.c         |  3 ++-
>  arch/x86/kvm/vmx/tdx.c          |  3 +++
>  3 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 32c7d58a5d68..df535f08e004 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1281,6 +1281,15 @@ enum kvm_apicv_inhibit {
>          */
>         APICV_INHIBIT_REASON_LOGICAL_ID_ALIASED,
>
> +       /*********************************************************/
> +       /* INHIBITs that are relevant only to the Intel's APICv. */
> +       /*********************************************************/
> +
> +       /*
> +        * APICv is disabled because TDX doesn't support it.
> +        */
> +       APICV_INHIBIT_REASON_TDX,
> +
>         NR_APICV_INHIBIT_REASONS,
>  };
>
> @@ -1299,7 +1308,8 @@ enum kvm_apicv_inhibit {
>         __APICV_INHIBIT_REASON(IRQWIN),                 \
>         __APICV_INHIBIT_REASON(PIT_REINJ),              \
>         __APICV_INHIBIT_REASON(SEV),                    \
> -       __APICV_INHIBIT_REASON(LOGICAL_ID_ALIASED)
> +       __APICV_INHIBIT_REASON(LOGICAL_ID_ALIASED),     \
> +       __APICV_INHIBIT_REASON(TDX)
>
>  struct kvm_arch {
>         unsigned long n_used_mmu_pages;
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 7f933f821188..13a0ab0a520c 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -445,7 +445,8 @@ static int vt_gmem_private_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn)
>          BIT(APICV_INHIBIT_REASON_BLOCKIRQ) |                   \
>          BIT(APICV_INHIBIT_REASON_PHYSICAL_ID_ALIASED) |        \
>          BIT(APICV_INHIBIT_REASON_APIC_ID_MODIFIED) |           \
> -        BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED))
> +        BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED) |         \
> +        BIT(APICV_INHIBIT_REASON_TDX))
>
>  struct kvm_x86_ops vt_x86_ops __initdata = {
>         .name = KBUILD_MODNAME,
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index b0f525069ebd..b51d2416acfb 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -2143,6 +2143,8 @@ static int __tdx_td_init(struct kvm *kvm, struct td_params *td_params,
>                 goto teardown;
>         }
>
> +       kvm_set_apicv_inhibit(kvm, APICV_INHIBIT_REASON_TDX);
> +
>         return 0;
>
>         /*
> @@ -2528,6 +2530,7 @@ static int tdx_td_vcpu_init(struct kvm_vcpu *vcpu, u64 vcpu_rcx)
>                 return -EIO;
>         }
>
> +       vcpu->arch.apic->apicv_active = false;

With this setting, apic_timer_expired[1] will always cause timer
interrupts to be pending without injecting them right away. Injecting
it after VM exit [2] could cause unbounded delays to timer interrupt
injection.

[1] https://git.kernel.org/pub/scm/virt/kvm/kvm.git/tree/arch/x86/kvm/lapic.c?h=kvm-coco-queue#n1922
[2] https://git.kernel.org/pub/scm/virt/kvm/kvm.git/tree/arch/x86/kvm/x86.c?h=kvm-coco-queue#n11263

>         vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
>
>         return 0;
> --
> 2.46.0
>
>