linux-kernel - Re: [RFC PATCH v5 086/104] KVM: TDX: handle ept violation/misconfig exit

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Message-ID: <CAAhR5DEb+jRfGxK0nv4A_XEEnY4yrw1CzCcXU8HNw=CnHW27Gw@mail.gmail.com>
Date:   Wed, 6 Apr 2022 13:50:06 -0700
From:   Sagi Shahar <sagis@...gle.com>
To:     "Yamahata, Isaku" <isaku.yamahata@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 086/104] KVM: TDX: handle ept violation/misconfig exit

On Fri, Mar 4, 2022 at 12:23 PM <isaku.yamahata@...el.com> wrote:
>
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> On EPT violation, call a common function, __vmx_handle_ept_violation() to
> trigger x86 MMU code.  On EPT misconfiguration, exit to ring 3 with
> KVM_EXIT_UNKNOWN.  because EPT misconfiguration can't happen as MMIO is
> trigged by TDG.VP.VMCALL. No point to set a misconfiguration value for the
> fast path.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  arch/x86/kvm/vmx/tdx.c | 40 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 38 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 6fbe89bcfe1e..2c35dcad077e 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1081,6 +1081,40 @@ void tdx_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,
>         __vmx_deliver_posted_interrupt(vcpu, &tdx->pi_desc, vector);
>  }
>
> +#define TDX_SEPT_PFERR (PFERR_WRITE_MASK | PFERR_USER_MASK)

TDX_SEPT_PFERR is defined using PFERR_.* bitmask but
__vmx_handle_ept_violation is accepting an EPT_VIOLATION_.* bitmask.
so (PFERR_WRITE_MASK | PFERR_USER_MASK) will get interpreted as
(EPT_VIOLATION_ACC_WRITE | EPT_VIOLATION_ACC_INSTR) which will get
translated to (PFERR_WRITE_MASK | PFERR_FETCH_MASK). Was that the
intention of this code?

> +
> +static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
> +{
> +       unsigned long exit_qual;
> +
> +       if (kvm_is_private_gpa(vcpu->kvm, tdexit_gpa(vcpu)))
> +               exit_qual = TDX_SEPT_PFERR;
> +       else {
> +               exit_qual = tdexit_exit_qual(vcpu);
> +               if (exit_qual & EPT_VIOLATION_ACC_INSTR) {
> +                       pr_warn("kvm: TDX instr fetch to shared GPA = 0x%lx @ RIP = 0x%lx\n",
> +                               tdexit_gpa(vcpu), kvm_rip_read(vcpu));
> +                       vcpu->run->exit_reason = KVM_EXIT_EXCEPTION;
> +                       vcpu->run->ex.exception = PF_VECTOR;
> +                       vcpu->run->ex.error_code = exit_qual;
> +                       return 0;
> +               }
> +       }
> +
> +       trace_kvm_page_fault(tdexit_gpa(vcpu), exit_qual);
> +       return __vmx_handle_ept_violation(vcpu, tdexit_gpa(vcpu), exit_qual);
> +}
> +
> +static int tdx_handle_ept_misconfig(struct kvm_vcpu *vcpu)
> +{
> +       WARN_ON(1);
> +
> +       vcpu->run->exit_reason = KVM_EXIT_UNKNOWN;
> +       vcpu->run->hw.hardware_exit_reason = EXIT_REASON_EPT_MISCONFIG;
> +
> +       return 0;
> +}
> +
>  int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
>  {
>         union tdx_exit_reason exit_reason = to_tdx(vcpu)->exit_reason;
> @@ -1097,6 +1131,10 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
>         WARN_ON_ONCE(fastpath != EXIT_FASTPATH_NONE);
>
>         switch (exit_reason.basic) {
> +       case EXIT_REASON_EPT_VIOLATION:
> +               return tdx_handle_ept_violation(vcpu);
> +       case EXIT_REASON_EPT_MISCONFIG:
> +               return tdx_handle_ept_misconfig(vcpu);
>         case EXIT_REASON_OTHER_SMI:
>                 /*
>                  * If reach here, it's not a MSMI.
> @@ -1378,8 +1416,6 @@ void tdx_flush_tlb(struct kvm_vcpu *vcpu)
>                 cpu_relax();
>  }
>
> -#define TDX_SEPT_PFERR (PFERR_WRITE_MASK | PFERR_USER_MASK)
> -
>  static int tdx_init_mem_region(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
>  {
>         struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> --
> 2.25.1
>

Sagi