linux-kernel - Re: [PATCH 4/8] kvm: vmx: Set IBPB when running a different VCPU

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Message-ID: <CANRm+Cwu+6TkA-dZaCJnMRY4PYMJ8JjQgegMPM8e6UqqJ+9Ohw@mail.gmail.com>
Date:   Fri, 12 Jan 2018 09:49:58 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm <kvm@...r.kernel.org>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Liran Alon <liran.alon@...cle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Anthony Liguori <aliguori@...zon.com>, thomas.lendacky@....com,
        dwmw@...zon.co.uk, Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [PATCH 4/8] kvm: vmx: Set IBPB when running a different VCPU

2018-01-09 20:03 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>
>         if (!already_loaded) {
> @@ -4029,6 +4031,13 @@ static void free_loaded_vmcs(struct loaded_vmcs *loaded_vmcs)
>         free_vmcs(loaded_vmcs->vmcs);
>         loaded_vmcs->vmcs = NULL;
>         WARN_ON(loaded_vmcs->shadow_vmcs != NULL);
> +
> +       /*
> +        * The VMCS could be recycled, causing a false negative in
> +        * vmx_vcpu_load; block speculative execution.
> +        */
> +       if (have_spec_ctrl)
> +               wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB);
>  }

Intel guys told us the recycle is about the address of vmcs, not the
content. Could you explain more why it matters?

Regards,
Wanpeng Li