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

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Date:   Wed, 1 Nov 2023 12:21:32 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Yang Weijiang <weijiang.yang@...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 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.