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    SubjectRe: [PATCH v19 110/130] KVM: TDX: Handle TDX PV MMIO hypercall
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    On 2/26/2024 4:26 PM, 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 55fc6cc6c816..389bb95d2af0 100644
    > --- a/arch/x86/kvm/vmx/tdx.c
    > +++ b/arch/x86/kvm/vmx/tdx.c
    > @@ -1217,6 +1217,118 @@ 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;
    > +
    > + KVM_BUG_ON(vcpu->mmio_needed != 1, vcpu->kvm);
    > + 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;
    > +
    > + KVM_BUG_ON(vcpu->mmio_needed, vcpu->kvm);
    > +
    > + 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. */
    Based on the discussion
    https://lore.kernel.org/all/ZcUO5sFEAIH68JIA@google.com/
    Do we still allow the MMIO without shared bit?

    > + gpa = gpa & ~gfn_to_gpa(kvm_gfn_shared_mask(vcpu->kvm));
    > +
    > + if (size > 8u || ((gpa + size - 1) ^ gpa) & PAGE_MASK)
    "size > 8u" can be removed, since based on the check of size above, it
    can't be greater than 8.


    > + 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)) {
    Should this be checked for write first?

    I check the handle_ept_misconfig() in VMX, it doesn't check write first
    neither.

    Functionally, it should be OK since guest will not read the address
    range of fast mmio.
    So the read case will be filtered out by ioeventfd_write().
    But it has take a long way to get to ioeventfd_write().
    Isn't it more efficient to check write first?


    > + 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, TDVMCALL_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, TDVMCALL_INVALID_OPERAND);
    > + return 1;
    > +}
    > +
    > static int handle_tdvmcall(struct kvm_vcpu *vcpu)
    > {
    > if (tdvmcall_exit_type(vcpu))
    > @@ -1229,6 +1341,8 @@ 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 03950368d8db..d5b18cad9dcd 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -13975,6 +13975,7 @@ EXPORT_SYMBOL_GPL(kvm_sev_es_string_io);
    >
    > 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 e27c22449d85..bc14e1f2610c 100644
    > --- a/virt/kvm/kvm_main.c
    > +++ b/virt/kvm/kvm_main.c
    > @@ -2689,6 +2689,7 @@ 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)
    > {
    > @@ -5992,6 +5993,7 @@ 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);
    >
    > int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
    > int len, struct kvm_io_device *dev)


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