Subject: Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and
 MSR_IA32_PRED_CMD down to the guest
To: Jim Mattson <jmattson@google.com>
Cc: Liran Alon <liran.alon@oracle.com>, dwmw@amazon.co.uk,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        the arch/x86 maintainers <x86@kernel.org>, bp@alien8.de,
        Nadav Amit <nadav.amit@gmail.com>,
        Tom Lendacky <thomas.lendacky@amd.com>, aliguori@amazon.com,
        Arjan van de Ven <arjan@linux.intel.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        kvm list <kvm@vger.kernel.org>
References: <c687a8eb-663d-48c1-9dc3-7f6b22973f81@default>
 <65578664-e3ec-f894-4e94-ff9fe6d7d6b3@redhat.com>
 <CALMp9eSj11tFeSRXDB5xAj6zPxNG=yoqOPbRNxkdjzgG3Cjc4w@mail.gmail.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <4ceeadb7-61c0-e5b9-867d-16c2bedcabc5@redhat.com>
Date: Wed, 10 Jan 2018 18:16:09 +0100
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On 10/01/2018 18:14, Jim Mattson wrote:
>>> If (a) is true, does "IBRS ALL THE TIME" usage is basically a CPU
>>> change to just create all BTB/BHB entries to be tagged with
>>> prediction-mode at creation-time and that tag to be compared to current
>>> prediction-mode when CPU attempts to use BTB/BHB?
>>
>> I hope so, and I hope said prediction mode includes PCID/VPID too.
>
> Branch prediction entries should probably be tagged with PCID, VPID,
> EP4TA, and thread ID...the same things used to tag TLB contexts.

But if so, I don't see the need for IBPB.

Paolo