From: Paolo Bonzini <pbonzini@redhat.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
x86@kernel.org, "Radim Krčmář" <rkrcmar@redhat.com>,
"KarimAllah Ahmed" <karahmed@amazon.de>,
"David Woodhouse" <dwmw@amazon.co.uk>,
"Jim Mattson" <jmattson@google.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@kernel.org>,
stable@vger.kernel.org
Subject: Re: [PATCH 1/3] KVM: x86: use native MSR ops for SPEC_CTRL
Date: Fri, 23 Feb 2018 10:37:49 +0100 [thread overview]
Message-ID: <d66a2358-cfac-f441-3b59-e44674b6a792@redhat.com> (raw)
In-Reply-To: <20180222170717.GP31483@char.us.oracle.com>
On 22/02/2018 18:07, Konrad Rzeszutek Wilk wrote:
>> Having a paravirt indirect call in the IBRS restore path is not a
>> good idea, since we are trying to protect from speculative execution
>> of bogus indirect branch targets. It is also slower, so use
>> native_wrmsrl on the vmentry path too.
> But it gets replaced during patching. As in once the machine boots
> the assembler changes from:
>
> callq *0xfffflbah
>
> to
> wrmsr
>
> ? I don't think you need this patch.
Why not be explicit? According to the spec, PRED_CMD and SPEC_CTRL
should be passed down to the guest without interception so it's safe to
do this. On the other hand, especially with nested virtualization, I
don't think you can absolutely guarantee that the paravirt call will be
patched to rdmsr/wrmsr.
Paolo
next prev parent reply other threads:[~2018-02-23 9:37 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-21 21:41 [PATCH 0/3] x86/pti: KVM: fixes and optimizations for IBRS Paolo Bonzini
2018-02-21 21:41 ` [PATCH 1/3] KVM: x86: use native MSR ops for SPEC_CTRL Paolo Bonzini
2018-02-21 23:49 ` Jim Mattson
2018-02-22 17:07 ` Konrad Rzeszutek Wilk
2018-02-23 9:37 ` Paolo Bonzini [this message]
2018-02-23 17:22 ` Konrad Rzeszutek Wilk
2018-02-23 17:35 ` Paolo Bonzini
2018-02-23 17:55 ` Konrad Rzeszutek Wilk
2018-02-21 21:41 ` [PATCH 2/3] KVM: nVMX: fix wrong condition for SPEC_CTRL and PRED_CMD MSRs Paolo Bonzini
2018-02-22 0:07 ` Jim Mattson
2018-02-22 9:39 ` Paolo Bonzini
2018-02-21 21:41 ` [PATCH 3/3] KVM: VMX: mark RDMSR path as unlikely Paolo Bonzini
2018-02-22 0:25 ` Jim Mattson
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