Re: [PATCH v19 101/130] KVM: TDX: handle ept violation/misconfig exit

[Chenyi Qiang]

On 2/26/2024 4:26 PM, isaku.yamahata@xxxxxxxxx wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> 
> On EPT violation, call a common function, __vmx_handle_ept_violation() to
> trigger x86 MMU code.  On EPT misconfiguration, exit to ring 3 with
> KVM_EXIT_UNKNOWN.  because EPT misconfiguration can't happen as MMIO is
> trigged by TDG.VP.VMCALL. No point to set a misconfiguration value for the

s/trigged/triggered

> fast path.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> 
> ---
> v14 -> v15:
> - use PFERR_GUEST_ENC_MASK to tell the fault is private
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

duplicated SOB

> ---
>  arch/x86/kvm/vmx/common.h |  3 +++
>  arch/x86/kvm/vmx/tdx.c    | 49 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/common.h b/arch/x86/kvm/vmx/common.h
> index 632af7a76d0a..027aa4175d2c 100644
> --- a/arch/x86/kvm/vmx/common.h
> +++ b/arch/x86/kvm/vmx/common.h
> @@ -87,6 +87,9 @@ static inline int __vmx_handle_ept_violation(struct kvm_vcpu *vcpu, gpa_t gpa,
>  	error_code |= (exit_qualification & EPT_VIOLATION_GVA_TRANSLATED) != 0 ?
>  	       PFERR_GUEST_FINAL_MASK : PFERR_GUEST_PAGE_MASK;
>  
> +	if (kvm_is_private_gpa(vcpu->kvm, gpa))
> +		error_code |= PFERR_GUEST_ENC_MASK;
> +
>  	return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
>  }
>  
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 2f68e6f2b53a..0db80fa020d2 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1285,6 +1285,51 @@ void tdx_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,
>  	__vmx_deliver_posted_interrupt(vcpu, &tdx->pi_desc, vector);
>  }
>  
> +static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
> +{
> +	unsigned long exit_qual;
> +
> +	if (kvm_is_private_gpa(vcpu->kvm, tdexit_gpa(vcpu))) {
> +		/*
> +		 * Always treat SEPT violations as write faults.  Ignore the
> +		 * EXIT_QUALIFICATION reported by TDX-SEAM for SEPT violations.
> +		 * TD private pages are always RWX in the SEPT tables,
> +		 * i.e. they're always mapped writable.  Just as importantly,
> +		 * treating SEPT violations as write faults is necessary to
> +		 * avoid COW allocations, which will cause TDAUGPAGE failures
> +		 * due to aliasing a single HPA to multiple GPAs.
> +		 */
> +#define TDX_SEPT_VIOLATION_EXIT_QUAL	EPT_VIOLATION_ACC_WRITE
> +		exit_qual = TDX_SEPT_VIOLATION_EXIT_QUAL;
> +	} else {
> +		exit_qual = tdexit_exit_qual(vcpu);
> +		if (exit_qual & EPT_VIOLATION_ACC_INSTR) {
> +			pr_warn("kvm: TDX instr fetch to shared GPA = 0x%lx @ RIP = 0x%lx\n",
> +				tdexit_gpa(vcpu), kvm_rip_read(vcpu));
> +			vcpu->run->exit_reason = KVM_EXIT_EXCEPTION;
> +			vcpu->run->ex.exception = PF_VECTOR;
> +			vcpu->run->ex.error_code = exit_qual;
> +			return 0;
> +		}
> +	}
> +
> +	trace_kvm_page_fault(vcpu, tdexit_gpa(vcpu), exit_qual);
> +	return __vmx_handle_ept_violation(vcpu, tdexit_gpa(vcpu), exit_qual);
> +}
> +
> +static int tdx_handle_ept_misconfig(struct kvm_vcpu *vcpu)
> +{
> +	WARN_ON_ONCE(1);
> +
> +	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> +	vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
> +	vcpu->run->internal.ndata = 2;
> +	vcpu->run->internal.data[0] = EXIT_REASON_EPT_MISCONFIG;
> +	vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
> +
> +	return 0;
> +}
> +
>  int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
>  {
>  	union tdx_exit_reason exit_reason = to_tdx(vcpu)->exit_reason;
> @@ -1345,6 +1390,10 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
>  	WARN_ON_ONCE(fastpath != EXIT_FASTPATH_NONE);
>  
>  	switch (exit_reason.basic) {
> +	case EXIT_REASON_EPT_VIOLATION:
> +		return tdx_handle_ept_violation(vcpu);
> +	case EXIT_REASON_EPT_MISCONFIG:
> +		return tdx_handle_ept_misconfig(vcpu);
>  	case EXIT_REASON_OTHER_SMI:
>  		/*
>  		 * If reach here, it's not a Machine Check System Management