linux-kernel - Re: [PATCH v1 4/6] KVM: x86: Add emulator helper for LASS violation check

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Message-ID: <ZJsqanMgqOp6M8j/@google.com>
Date:   Tue, 27 Jun 2023 11:28:58 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Zeng Guang <guang.zeng@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        H Peter Anvin <hpa@...or.com>, kvm@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/6] KVM: x86: Add emulator helper for LASS violation check

On Thu, Jun 01, 2023, Zeng Guang wrote:
> When LASS is enabled, KVM need apply LASS violation check to instruction
> emulations. Add helper for the usage of x86 emulator to perform LASS
> protection.
> 
> Signed-off-by: Zeng Guang <guang.zeng@...el.com>
> Tested-by: Xuelian Guo <xuelian.guo@...el.com>
> ---
>  arch/x86/kvm/kvm_emulate.h |  1 +
>  arch/x86/kvm/x86.c         | 12 ++++++++++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
> index f1439ab7c14b..fd1c2b22867e 100644
> --- a/arch/x86/kvm/kvm_emulate.h
> +++ b/arch/x86/kvm/kvm_emulate.h
> @@ -230,6 +230,7 @@ struct x86_emulate_ops {
>  	int (*leave_smm)(struct x86_emulate_ctxt *ctxt);
>  	void (*triple_fault)(struct x86_emulate_ctxt *ctxt);
>  	int (*set_xcr)(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr);
> +	bool (*check_lass)(struct x86_emulate_ctxt *ctxt, u64 access, u64 la, u32 flags);
>  };
>  
>  /* Type, address-of, and value of an instruction's operand. */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c0778ca39650..faf01fecc4ca 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8287,6 +8287,17 @@ static void emulator_vm_bugged(struct x86_emulate_ctxt *ctxt)
>  		kvm_vm_bugged(kvm);
>  }
>  
> +static bool emulator_check_lass(struct x86_emulate_ctxt *ctxt,
> +				u64 access, u64 la, u32 flags)
> +{
> +	struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
> +
> +	if (!is_long_mode(vcpu))
> +		return false;

Likely a moot point if we wrap ->gva_to_gpa(), but most this into the vendor
implementation.

And if we keep these emulator hooks, massage the patch ordering:

  1. Add plumbing to emulator to pass new flags
  2. Add kvm_x86_ops definition and invocation from emulator
  3. Implement and wire up vmx_is_lass_violation()

That way the changes to each area of KVM are better isolated.

> +	return static_call(kvm_x86_check_lass)(vcpu, access, la, flags);
> +}
> +
>  static const struct x86_emulate_ops emulate_ops = {
>  	.vm_bugged           = emulator_vm_bugged,
>  	.read_gpr            = emulator_read_gpr,
> @@ -8332,6 +8343,7 @@ static const struct x86_emulate_ops emulate_ops = {
>  	.leave_smm           = emulator_leave_smm,
>  	.triple_fault        = emulator_triple_fault,
>  	.set_xcr             = emulator_set_xcr,
> +	.check_lass          = emulator_check_lass,
>  };
>  
>  static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
> -- 
> 2.27.0
>