From: Liran Alon <liran.alon@oracle.com>
To: <pbonzini@redhat.com>
Cc: <jmattson@google.com>, <x86@kernel.org>, <dwmw@amazon.co.uk>,
<bp@alien8.de>, <thomas.lendacky@amd.com>, <aliguori@amazon.com>,
<rkrcmar@redhat.com>, <linux-kernel@vger.kernel.org>,
<kvm@vger.kernel.org>
Subject: Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD down to the guest
Date: Tue, 9 Jan 2018 16:33:47 -0800 (PST) [thread overview]
Message-ID: <9e95b190-31e3-4a9a-9efe-8d153a81cf46@default> (raw)
----- pbonzini@redhat.com wrote:
> On 09/01/2018 17:48, Liran Alon wrote:
> >>>
> >>> + if (have_spec_ctrl) {
> >>> + rdmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);
> >>> + if (vmx->spec_ctrl != 0)
> >>> + wrmsrl(MSR_IA32_SPEC_CTRL, 0);
> >
> > As I said also on the AMD patch, I think this is a bug.
> > Intel specify that we should set IBRS bit even if it was already set
> on every #VMExit.
>
> That's correct (though I'd like to understand _why_---I'm not
> inclined
> to blindly trust a spec), but for now it's saving a wrmsr of 0. That
> is
> quite obviously okay, and will be also okay after the bare-metal IBRS
> patches.
>
> Of course the code will become something like
>
> if (using_ibrs || vmx->spec_ctrl != 0)
> wrmsrl(MSR_IA32_SPEC_CTRL, host_ibrs);
>
> optimizing the case where the host is using retpolines.
>
> Paolo
I agree with all the above.
-Liran
next reply other threads:[~2018-01-10 0:39 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-10 0:33 Liran Alon [this message]
-- strict thread matches above, loose matches on Subject: below --
2018-01-10 16:51 Liran Alon
2018-01-10 17:07 ` David Woodhouse
2018-01-10 16:19 Liran Alon
2018-01-10 16:27 ` Paolo Bonzini
2018-01-10 17:14 ` Jim Mattson
2018-01-10 17:16 ` Paolo Bonzini
2018-01-10 17:23 ` Nadav Amit
2018-01-10 17:32 ` Jim Mattson
2018-01-10 16:47 ` David Woodhouse
2018-01-09 16:48 Liran Alon
2018-01-09 16:57 ` Paolo Bonzini
2018-01-10 5:03 ` Nadav Amit
2018-01-10 13:20 ` Paolo Bonzini
2018-01-10 14:06 ` Arjan van de Ven
2018-01-10 14:28 ` Paolo Bonzini
2018-01-10 15:41 ` Konrad Rzeszutek Wilk
2018-01-10 15:45 ` Paolo Bonzini
2018-01-10 15:48 ` Woodhouse, David
2018-01-10 15:56 ` Paolo Bonzini
2018-01-10 16:05 ` David Woodhouse
2018-01-12 23:17 ` Jim Mattson
2018-01-12 23:19 ` Nadav Amit
2018-01-09 16:06 Liran Alon
2018-01-09 12:03 [PATCH v2 0/8] KVM: x86: expose CVE-2017-5715 ("Spectre variant 2") mitigations to guest Paolo Bonzini
2018-01-09 12:03 ` [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD down to the guest Paolo Bonzini
2018-01-13 10:16 ` Longpeng (Mike)
2018-01-15 9:23 ` Paolo Bonzini
2018-01-15 9:34 ` Thomas Gleixner
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