linux-kernel - Re: [PATCH 2/3] x86/split_lock: Refactor and export handle_user_split

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Date:   Fri, 10 Apr 2020 12:21:36 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     x86@...nel.org, "Kenneth R . Crudup" <kenny@...ix.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Nadav Amit <namit@...are.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jessica Yu <jeyu@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86/split_lock: Refactor and export
 handle_user_split_lock() for KVM

On 10/04/20 06:39, Xiaoyao Li wrote:
> 
>   +static bool guest_handles_ac(struct kvm_vcpu *vcpu)
> +{
> +    /*
> +     * If guest has alignment checking enabled in CR0 and activated in
> +     * eflags, then the #AC originated from CPL3 and the guest is able
> +     * to handle it. It does not matter whether this is a regular or
> +     * a split lock operation induced #AC.
> +     */
> +    if (vmx_get_cpl(vcpu) == 3 && kvm_read_cr0_bits(vcpu, X86_CR0_AM) &&
> +        kvm_get_rflags(vcpu) & X86_EFLAGS_AC)
> +        return true;
> +
> +    /* Add guest SLD handling checks here once it's supported */
> +    return false;
> +}
> +
>   static int handle_exception_nmi(struct kvm_vcpu *vcpu)
>   {
>       struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -4630,6 +4647,7 @@ static int handle_exception_nmi(struct k
>       u32 intr_info, ex_no, error_code;
>       unsigned long cr2, rip, dr6;
>       u32 vect_info;
> +    int err;
>         vect_info = vmx->idt_vectoring_info;
>       intr_info = vmx->exit_intr_info;
> @@ -4688,9 +4706,6 @@ static int handle_exception_nmi(struct k
>           return handle_rmode_exception(vcpu, ex_no, error_code);
>         switch (ex_no) {
> -    case AC_VECTOR:
> -        kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
> -        return 1;
>       case DB_VECTOR:
>           dr6 = vmcs_readl(EXIT_QUALIFICATION);
>           if (!(vcpu->guest_debug &
> @@ -4719,6 +4734,29 @@ static int handle_exception_nmi(struct k
>           kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip;
>           kvm_run->debug.arch.exception = ex_no;
>           break;
> +    case AC_VECTOR:
> +        if (guest_handles_ac(vcpu)) {
> +            kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
> +            return 1;
> +        }
> +        /*
> +         * Handle #AC caused by split lock detection. If the host
> +         * mode is sld_warn, then it warns, marks current with
> +         * TIF_SLD and disables split lock detection. So the guest
> +         * can just continue.
> +         *
> +         * If the host mode is fatal, the handling code warned. Let
> +         * qemu kill itself.
> +         *
> +         * If the host mode is off, then this #AC is bonkers and
> +         * something is badly wrong. Let it fail as well.
> +         */
> +        err = handle_ac_split_lock(kvm_rip_read(vcpu));
> +        if (!err)
> +            return 1;
> +        /* Propagate the error type to user space */
> +        error_code = err == -EFAULT ? 0x100 : 0x200;
> +        fallthrough;


Acked-by: Paolo Bonzini <pbonzini@...hat.com>