linux-kernel - Re: [PATCH 10/18] KVM: x86: Keep track of instruction length during faults

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Message-ID: <ZuSOFJJbkp1cNdsJ@google.com>
Date: Fri, 13 Sep 2024 12:10:12 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Nicolas Saenz Julienne <nsaenz@...zon.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, pbonzini@...hat.com, 
	vkuznets@...hat.com, linux-doc@...r.kernel.org, linux-hyperv@...r.kernel.org, 
	linux-arch@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	graf@...zon.de, dwmw2@...radead.org, paul@...zon.com, mlevitsk@...hat.com, 
	jgowans@...zon.com, corbet@....net, decui@...rosoft.com, tglx@...utronix.de, 
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, 
	amoorthy@...gle.com
Subject: Re: [PATCH 10/18] KVM: x86: Keep track of instruction length during faults

On Sun, Jun 09, 2024, Nicolas Saenz Julienne wrote:
> Both VMX and SVM provide the length of the instruction
> being run at the time of the page fault. Save it within 'struct
> kvm_page_fault', as it'll become useful in the future.

Nit, please wrap closer to 75 characters.

> Signed-off-by: Nicolas Saenz Julienne <nsaenz@...zon.com>
> ---
>  arch/x86/kvm/mmu/mmu.c          | 11 ++++++++---
>  arch/x86/kvm/mmu/mmu_internal.h |  5 ++++-
>  arch/x86/kvm/vmx/vmx.c          | 16 ++++++++++++++--
>  3 files changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 8d74bdef68c1d..39b113afefdfc 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4271,7 +4271,8 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
>  	      work->arch.cr3 != kvm_mmu_get_guest_pgd(vcpu, vcpu->arch.mmu))
>  		return;
>  
> -	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, work->arch.error_code, true, NULL);
> +	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, work->arch.error_code,
> +			      true, NULL, 0);

Hrm, I just proposed adding another (out) parameter to kvm_mmu_do_page_fault()
in the TDX series[*], I wonder if we're reaching the point where it makes sense
to have kvm_mmu_do_page_fault() take a struct too.

[*] https://lore.kernel.org/all/ZuR09EqzU1WbQYGd@google.com

> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index ac0682fece604..9ba38e0b0c7a8 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5807,11 +5807,13 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
>  	if (unlikely(allow_smaller_maxphyaddr && !kvm_vcpu_is_legal_gpa(vcpu, gpa)))
>  		return kvm_emulate_instruction(vcpu, 0);
>  
> -	return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
> +	return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL,
> +				  vmcs_read32(VM_EXIT_INSTRUCTION_LEN));

It might be worth adding a cached EXREG for instruction length, e.g.
VCPU_EXREG_EXIT_INFO_3 + vmx_get_insn_len(), similar to how for vmx_get_exit_qual()
and vmx_get_intr_info() pair up with VCPU_EXREG_EXIT_INFO_{1,2}.