linux-kernel - Re: [PATCH v6 24/25] KVM: nVMX: Introduce new VMX_BASIC bit for event error

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Date:   Wed, 15 Nov 2023 16:31:25 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Chao Gao <chao.gao@...el.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <dave.hansen@...el.com>,
        <peterz@...radead.org>, <rick.p.edgecombe@...el.com>,
        <john.allen@....com>
Subject: Re: [PATCH v6 24/25] KVM: nVMX: Introduce new VMX_BASIC bit for event
 error_code delivery to L1

On 11/1/2023 12:21 PM, Chao Gao wrote:
> On Thu, Sep 14, 2023 at 02:33:24AM -0400, Yang Weijiang wrote:
>> Per SDM description(Vol.3D, Appendix A.1):
>> "If bit 56 is read as 1, software can use VM entry to deliver a hardware
>> exception with or without an error code, regardless of vector"
>>
>> Modify has_error_code check before inject events to nested guest. Only
>> enforce the check when guest is in real mode, the exception is not hard
>> exception and the platform doesn't enumerate bit56 in VMX_BASIC, in all
>> other case ignore the check to make the logic consistent with SDM.
>>
>> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
>> ---
>> arch/x86/kvm/vmx/nested.c | 22 ++++++++++++++--------
>> arch/x86/kvm/vmx/nested.h |  5 +++++
>> 2 files changed, 19 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>> index c5ec0ef51ff7..78a3be394d00 100644
>> --- a/arch/x86/kvm/vmx/nested.c
>> +++ b/arch/x86/kvm/vmx/nested.c
>> @@ -1205,9 +1205,9 @@ static int vmx_restore_vmx_basic(struct vcpu_vmx *vmx, u64 data)
>> {
>> 	const u64 feature_and_reserved =
>> 		/* feature (except bit 48; see below) */
>> -		BIT_ULL(49) | BIT_ULL(54) | BIT_ULL(55) |
>> +		BIT_ULL(49) | BIT_ULL(54) | BIT_ULL(55) | BIT_ULL(56) |
>> 		/* reserved */
>> -		BIT_ULL(31) | GENMASK_ULL(47, 45) | GENMASK_ULL(63, 56);
>> +		BIT_ULL(31) | GENMASK_ULL(47, 45) | GENMASK_ULL(63, 57);
>> 	u64 vmx_basic = vmcs_config.nested.basic;
>>
>> 	if (!is_bitwise_subset(vmx_basic, data, feature_and_reserved))
>> @@ -2846,12 +2846,16 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
>> 		    CC(intr_type == INTR_TYPE_OTHER_EVENT && vector != 0))
>> 			return -EINVAL;
>>
>> -		/* VM-entry interruption-info field: deliver error code */
>> -		should_have_error_code =
>> -			intr_type == INTR_TYPE_HARD_EXCEPTION && prot_mode &&
>> -			x86_exception_has_error_code(vector);
>> -		if (CC(has_error_code != should_have_error_code))
>> -			return -EINVAL;
>> +		if (!prot_mode || intr_type != INTR_TYPE_HARD_EXCEPTION ||
>> +		    !nested_cpu_has_no_hw_errcode_cc(vcpu)) {
>> +			/* VM-entry interruption-info field: deliver error code */
>> +			should_have_error_code =
>> +				intr_type == INTR_TYPE_HARD_EXCEPTION &&
>> +				prot_mode &&
>> +				x86_exception_has_error_code(vector);
>> +			if (CC(has_error_code != should_have_error_code))
>> +				return -EINVAL;
>> +		}
> prot_mode and intr_type are used twice, making the code a little hard to read.
>
> how about:
> 		/*
> 		 * Cannot deliver error code in real mode or if the
> 		 * interruption type is not hardware exception. For other
> 		 * cases, do the consistency check only if the vCPU doesn't
> 		 * enumerate VMX_BASIC_NO_HW_ERROR_CODE_CC.
> 		 */
> 		if (!prot_mode || intr_type != INTR_TYPE_HARD_EXCEPTION) {
> 			if (CC(has_error_code))
> 				return -EINVAL;
> 		} else if (!nested_cpu_has_no_hw_errcode_cc(vcpu)) {
> 			if (CC(has_error_code != x86_exception_has_error_code(vector)))
> 				return -EINVAL;
> 		}
>
> and drop should_have_error_code.

The change looks clearer, I'll take it, thanks!