Re: [PATCH v19 110/130] KVM: TDX: Handle TDX PV MMIO hypercall

[Binbin Wu]

On 2/26/2024 4:26 PM, isaku.yamahata@xxxxxxxxx wrote:
> From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
>
> 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@xxxxxxxxx>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>   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;
mmio_needed is used by instruction emulator to setup the complete callback.
Since TDX handle MMIO in a PV way, mmio_needed is not needed here.

> +
> +	if (!vcpu->mmio_is_write) {
It's also needed by instruction emulator, we can use 
vcpu->run->mmio.is_write instead.

> +		gpa = vcpu->mmio_fragments[0].gpa;
> +		size = vcpu->mmio_fragments[0].len;

Since MMIO cross page boundary is not allowed according to the input 
checks from TDVMCALL, these mmio_fragments[] is not needed.
Just use vcpu->run->mmio.phys_addr and vcpu->run->mmio.len?

> +
> +		memcpy(&val, vcpu->run->mmio.data, size);
> +		tdvmcall_set_return_val(vcpu, val);
> +		trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
> +	}

Tracepoint for KVM_TRACE_MMIO_WRITE is missing when it is handled in 
userspace.

Also, the return code is only set when the emulation is done in kernel, 
but not set when it's handled in userspace.

> +	return 1;
> +}

How about the fixup as following:

@@ -1173,19 +1173,18 @@ static int tdx_emulate_io(struct kvm_vcpu *vcpu) 
static int tdx_complete_mmio(struct kvm_vcpu *vcpu) { unsigned long val 
= 0; - gpa_t gpa; - int size; - - vcpu->mmio_needed = 0; - - if 
(!vcpu->mmio_is_write) { - gpa = vcpu->mmio_fragments[0].gpa; - size = 
vcpu->mmio_fragments[0].len; + gpa_t gpa = vcpu->run->mmio.phys_addr; + 
int size = vcpu->run->mmio.len; + if (vcpu->run->mmio.is_write) { + 
trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, size, gpa, &val); + } else { 
memcpy(&val, vcpu->run->mmio.data, size); tdvmcall_set_return_val(vcpu, 
val); trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val); } + + 
tdvmcall_set_return_code(vcpu, TDVMCALL_SUCCESS); 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);
> +
[...]
> +
> +	/* Request the device emulation to userspace device model. */
> +	vcpu->mmio_needed = 1;
> +	vcpu->mmio_is_write = write;
Then they can be dropped.


> +	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;
These two lines can be dropped as well.

> +		trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, size, gpa, NULL);
> +	}
> +	return 0;
> +
> +error:
> +	tdvmcall_set_return_code(vcpu, TDVMCALL_INVALID_OPERAND);
> +	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; @@ -1265,13 +1272,11 @@ static int 
tdx_emulate_mmio(struct kvm_vcpu *vcpu) vcpu->run->mmio.is_write = 
write; vcpu->run->exit_reason = KVM_EXIT_MMIO; - if (write) { + if 
(write) memcpy(vcpu->run->mmio.data, &val, size); - } else { - 
vcpu->mmio_fragments[0].gpa = gpa; - vcpu->mmio_fragments[0].len = size; 
+ else trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, size, gpa, NULL); 
- } + return 0;