linux-kernel - Re: [RFC PATCH v5 102/104] KVM: TDX: Add methods to ignore accesses to CPU state

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Message-ID: <59376a41-65a9-0efa-dad6-b5906d89fb3c@intel.com>
Date:   Tue, 12 Apr 2022 15:31:48 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, isaku.yamahata@...el.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...il.com, Jim Mattson <jmattson@...gle.com>,
        erdemaktas@...gle.com, Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 102/104] KVM: TDX: Add methods to ignore accesses
 to CPU state

On 4/12/2022 2:52 PM, Paolo Bonzini wrote:
> On 4/12/22 08:49, Xiaoyao Li wrote:
>>
>>> +void tdx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
>>> +{
>>> +    kvm_register_mark_available(vcpu, reg);
>>> +    switch (reg) {
>>> +    case VCPU_REGS_RSP:
>>> +    case VCPU_REGS_RIP:
>>> +    case VCPU_EXREG_PDPTR:
>>> +    case VCPU_EXREG_CR0:
>>> +    case VCPU_EXREG_CR3:
>>> +    case VCPU_EXREG_CR4:
>>> +        break;
>>> +    default:
>>> +        KVM_BUG_ON(1, vcpu->kvm);
>>> +        break;
>>> +    }
>>> +}
>>
>> Isaku,
>>
>> We missed one case that some GPRs are accessible by KVM/userspace for 
>> TDVMCALL exit.
> 
> If a register is not in the VMX_REGS_LAZY_LOAD_SET it will never be 
> passed to tdx_cache_reg.  As far as I understand those TDVMCALL 
> registers do not include either RSP or RIP.

Sorry, I should not keep the code snippet of tdx_cache_reg() as 
reference to mislead you and other people.

I just want to remind that in the certain case of TDVMCALL, GPRs might 
be accessible.

> Paolo
>