linux-kernel - Re: [PATCH v19 109/130] KVM: TDX: Handle TDX PV port io hypercall

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Message-ID: <e7233d96-2ab1-4684-8ce4-0189a78339ca@linux.intel.com>
Date: Tue, 9 Jul 2024 14:26:35 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Isaku Yamahata <isaku.yamahata@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
 isaku.yamahata@...ux.intel.com, Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Reinette Chatre <reinette.chatre@...el.com>
Subject: Re: [PATCH v19 109/130] KVM: TDX: Handle TDX PV port io hypercall



On 4/18/2024 4:10 AM, Isaku Yamahata wrote:
> On Wed, Apr 17, 2024 at 08:51:39PM +0800,
> Binbin Wu <binbin.wu@...ux.intel.com> wrote:
>
>>
>> On 2/26/2024 4:26 PM, isaku.yamahata@...el.com wrote:
>>> From: Isaku Yamahata <isaku.yamahata@...el.com>
>>>
>>> Wire up TDX PV port IO hypercall to the KVM backend function.
>>>
>>> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
>>> Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
>>> ---
>>> v18:
>>> - Fix out case to set R10 and R11 correctly when user space handled port
>>>     out.
>>> ---
>>>    arch/x86/kvm/vmx/tdx.c | 67 ++++++++++++++++++++++++++++++++++++++++++
>>>    1 file changed, 67 insertions(+)
>>>
>>> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
>>> index a2caf2ae838c..55fc6cc6c816 100644
>>> --- a/arch/x86/kvm/vmx/tdx.c
>>> +++ b/arch/x86/kvm/vmx/tdx.c
>>> @@ -1152,6 +1152,71 @@ static int tdx_emulate_hlt(struct kvm_vcpu *vcpu)
>>>    	return kvm_emulate_halt_noskip(vcpu);
>>>    }
>>> +static int tdx_complete_pio_out(struct kvm_vcpu *vcpu)
>>> +{
>>> +	tdvmcall_set_return_code(vcpu, TDVMCALL_SUCCESS);
>>> +	tdvmcall_set_return_val(vcpu, 0);
>>> +	return 1;
>>> +}
>>> +
>>> +static int tdx_complete_pio_in(struct kvm_vcpu *vcpu)
>>> +{
>>> +	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
>>> +	unsigned long val = 0;
>>> +	int ret;
>>> +
>>> +	WARN_ON_ONCE(vcpu->arch.pio.count != 1);
>>> +
>>> +	ret = ctxt->ops->pio_in_emulated(ctxt, vcpu->arch.pio.size,
>>> +					 vcpu->arch.pio.port, &val, 1);
>>> +	WARN_ON_ONCE(!ret);
>>> +
>>> +	tdvmcall_set_return_code(vcpu, TDVMCALL_SUCCESS);
>>> +	tdvmcall_set_return_val(vcpu, val);
>>> +
>>> +	return 1;
>>> +}
>>> +
>>> +static int tdx_emulate_io(struct kvm_vcpu *vcpu)
>>> +{
>>> +	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
>>> +	unsigned long val = 0;
>>> +	unsigned int port;
>>> +	int size, ret;
>>> +	bool write;
>>> +
>>> +	++vcpu->stat.io_exits;
>>> +
>>> +	size = tdvmcall_a0_read(vcpu);
>>> +	write = tdvmcall_a1_read(vcpu);
>>> +	port = tdvmcall_a2_read(vcpu);
>>> +
>>> +	if (size != 1 && size != 2 && size != 4) {
>>> +		tdvmcall_set_return_code(vcpu, TDVMCALL_INVALID_OPERAND);
>>> +		return 1;
>>> +	}
>>> +
>>> +	if (write) {
>>> +		val = tdvmcall_a3_read(vcpu);
>>> +		ret = ctxt->ops->pio_out_emulated(ctxt, size, port, &val, 1);
>>> +
>>> +		/* No need for a complete_userspace_io callback. */
>> I am confused about the comment.
>>
>> The code below sets the complete_userspace_io callback for write case,
>> i.e. tdx_complete_pio_out().
> You're correct. This comment is stale and should be removed it.
Also, since the tdx_complete_pio_out() is installed as 
complete_userspace_io callback for write, it's more reasonable to move 
the reset of pio.count into tdx_complete_pio_out().
How about the following fixup:

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 9ead46cb75ab..b43bb8ccddb9 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1115,6 +1115,7 @@ static int tdx_emulate_hlt(struct kvm_vcpu *vcpu)

  static int tdx_complete_pio_out(struct kvm_vcpu *vcpu)
  {
+       vcpu->arch.pio.count = 0;
         tdvmcall_set_return_code(vcpu, TDVMCALL_SUCCESS);
         tdvmcall_set_return_val(vcpu, 0);
         return 1;
@@ -1159,15 +1160,13 @@ static int tdx_emulate_io(struct kvm_vcpu *vcpu)
         if (write) {
                 val = tdvmcall_a3_read(vcpu);
                 ret = ctxt->ops->pio_out_emulated(ctxt, size, port, 
&val, 1);
-
-               /* No need for a complete_userspace_io callback. */
-               vcpu->arch.pio.count = 0;
-       } else
+       } else {
                 ret = ctxt->ops->pio_in_emulated(ctxt, size, port, 
&val, 1);
+       }

-       if (ret)
+       if (ret) {
                 tdvmcall_set_return_val(vcpu, val);
-       else {
+       } else {
                 if (write)
                         vcpu->arch.complete_userspace_io = 
tdx_complete_pio_out;
                 else