Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <cover.1651774250.git.isaku.yamahata@intel.com> <ea5e6a1fc740cfe69167c8713b63fdb952a98e8b.1651774251.git.isaku.yamahata@intel.com>
In-Reply-To: <ea5e6a1fc740cfe69167c8713b63fdb952a98e8b.1651774251.git.isaku.yamahata@intel.com>
From:   Sagi Shahar <sagis@google.com>
Date:   Tue, 14 Jun 2022 11:08:16 -0700
Message-ID: <CAAhR5DGHhPagnaiC=Bn9v0qhNQ5N9HjsrDyQkv4dtui7dfMAbA@mail.gmail.com>
Subject: Re: [RFC PATCH v6 093/104] KVM: TDX: Handle TDX PV MMIO hypercall
To:     "Yamahata, Isaku" <isaku.yamahata@intel.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        isaku.yamahata@gmail.com, Paolo Bonzini <pbonzini@redhat.com>,
        Erdem Aktas <erdemaktas@google.com>,
        Sean Christopherson <seanjc@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, May 5, 2022 at 11:16 AM <isaku.yamahata@intel.com> wrote:
>
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> Export kvm_io_bus_read and kvm_mmio tracepoint and wire up TDX PV MMIO
> hypercall to the KVM backend functions.
>
> kvm_io_bus_read/write() searches KVM device emulated in kernel of the given
> MMIO address and emulates the MMIO.  As TDX PV MMIO also needs it, export
> kvm_io_bus_read().  kvm_io_bus_write() is already exported.  TDX PV MMIO
> emulates some of MMIO itself.  To add trace point consistently with x86
> kvm, export kvm_mmio tracepoint.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/vmx/tdx.c | 114 +++++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/x86.c     |   1 +
>  virt/kvm/kvm_main.c    |   2 +
>  3 files changed, 117 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index ee0cf5336ade..6ab4a52fc9e9 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1057,6 +1057,118 @@ static int tdx_emulate_io(struct kvm_vcpu *vcpu)
>         return ret;
>  }
>
> +static int tdx_complete_mmio(struct kvm_vcpu *vcpu)
> +{
> +       unsigned long val = 0;
> +       gpa_t gpa;
> +       int size;
> +
> +       WARN_ON(vcpu->mmio_needed != 1);
> +       vcpu->mmio_needed = 0;
> +
> +       if (!vcpu->mmio_is_write) {
> +               gpa = vcpu->mmio_fragments[0].gpa;
> +               size = vcpu->mmio_fragments[0].len;
> +
> +               memcpy(&val, vcpu->run->mmio.data, size);
> +               tdvmcall_set_return_val(vcpu, val);
> +               trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
> +       }
> +       return 1;
> +}
> +
> +static inline int tdx_mmio_write(struct kvm_vcpu *vcpu, gpa_t gpa, int size,
> +                                unsigned long val)
> +{
> +       if (kvm_iodevice_write(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
> +           kvm_io_bus_write(vcpu, KVM_MMIO_BUS, gpa, size, &val))
> +               return -EOPNOTSUPP;
> +
> +       trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, size, gpa, &val);
> +       return 0;
> +}
> +
> +static inline int tdx_mmio_read(struct kvm_vcpu *vcpu, gpa_t gpa, int size)
> +{
> +       unsigned long val;
> +
> +       if (kvm_iodevice_read(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
> +           kvm_io_bus_read(vcpu, KVM_MMIO_BUS, gpa, size, &val))
> +               return -EOPNOTSUPP;
> +
> +       tdvmcall_set_return_val(vcpu, val);
> +       trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
> +       return 0;
> +}
> +
> +static int tdx_emulate_mmio(struct kvm_vcpu *vcpu)
> +{
> +       struct kvm_memory_slot *slot;
> +       int size, write, r;
> +       unsigned long val;
> +       gpa_t gpa;
> +
> +       WARN_ON(vcpu->mmio_needed);
> +
> +       size = tdvmcall_a0_read(vcpu);
> +       write = tdvmcall_a1_read(vcpu);
> +       gpa = tdvmcall_a2_read(vcpu);
> +       val = write ? tdvmcall_a3_read(vcpu) : 0;
> +
> +       if (size != 1 && size != 2 && size != 4 && size != 8)
> +               goto error;
> +       if (write != 0 && write != 1)
> +               goto error;
> +
> +       /* Strip the shared bit, allow MMIO with and without it set. */
> +       gpa = gpa & ~gfn_to_gpa(kvm_gfn_shared_mask(vcpu->kvm));
> +
> +       if (size > 8u || ((gpa + size - 1) ^ gpa) & PAGE_MASK)
> +               goto error;
> +
> +       slot = kvm_vcpu_gfn_to_memslot(vcpu, gpa_to_gfn(gpa));
> +       if (slot && !(slot->flags & KVM_MEMSLOT_INVALID))
> +               goto error;
> +
> +       if (!kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) {
> +               trace_kvm_fast_mmio(gpa);
> +               return 1;
> +       }
> +
> +       if (write)
> +               r = tdx_mmio_write(vcpu, gpa, size, val);
> +       else
> +               r = tdx_mmio_read(vcpu, gpa, size);
> +       if (!r) {
> +               /* Kernel completed device emulation. */
> +               tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);
> +               return 1;
> +       }
> +
> +       /* Request the device emulation to userspace device model. */
> +       vcpu->mmio_needed = 1;
> +       vcpu->mmio_is_write = write;
> +       vcpu->arch.complete_userspace_io = tdx_complete_mmio;
> +
> +       vcpu->run->mmio.phys_addr = gpa;
> +       vcpu->run->mmio.len = size;
> +       vcpu->run->mmio.is_write = write;
> +       vcpu->run->exit_reason = KVM_EXIT_MMIO;
> +
> +       if (write) {
> +               memcpy(vcpu->run->mmio.data, &val, size);
> +       } else {
> +               vcpu->mmio_fragments[0].gpa = gpa;
> +               vcpu->mmio_fragments[0].len = size;
> +               trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, size, gpa, NULL);
> +       }
> +       return 0;
> +
> +error:
> +       tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);

We should return an error code here.

> +       return 1;
> +}
> +
>  static int handle_tdvmcall(struct kvm_vcpu *vcpu)
>  {
>         if (tdvmcall_exit_type(vcpu))
> @@ -1069,6 +1181,8 @@ static int handle_tdvmcall(struct kvm_vcpu *vcpu)
>                 return tdx_emulate_hlt(vcpu);
>         case EXIT_REASON_IO_INSTRUCTION:
>                 return tdx_emulate_io(vcpu);
> +       case EXIT_REASON_EPT_VIOLATION:
> +               return tdx_emulate_mmio(vcpu);
>         default:
>                 break;
>         }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5f291470a6f6..f367d0dcef97 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -13166,6 +13166,7 @@ bool kvm_arch_dirty_log_supported(struct kvm *kvm)
>
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_entry);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
> +EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_mmio);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_page_fault);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 4bf7178e42bd..7f01131666de 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2294,6 +2294,7 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn
>
>         return NULL;
>  }
> +EXPORT_SYMBOL_GPL(kvm_vcpu_gfn_to_memslot);
>
>  bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
>  {
> @@ -5169,6 +5170,7 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
>         r = __kvm_io_bus_read(vcpu, bus, &range, val);
>         return r < 0 ? r : 0;
>  }
> +EXPORT_SYMBOL_GPL(kvm_io_bus_read);
>
>  /* Caller must hold slots_lock. */
>  int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> --
> 2.25.1
>

Sagi