From: Paolo Bonzini <pbonzini@redhat.com>
To: "Zhang, Yang Z" <yang.z.zhang@intel.com>,
Wanpeng Li <wanpeng.li@linux.intel.com>,
Jan Kiszka <jan.kiszka@siemens.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
Gleb Natapov <gleb@kernel.org>, Bandan Das <bsd@redhat.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: nVMX: nested TPR shadow/threshold emulation
Date: Fri, 01 Aug 2014 08:35:03 +0200 [thread overview]
Message-ID: <53DB3517.1010408@redhat.com> (raw)
In-Reply-To: <A9667DDFB95DB7438FA9D7D576C3D87E0AB4D3F5@SHSMSX104.ccr.corp.intel.com>
Il 01/08/2014 02:57, Zhang, Yang Z ha scritto:
> > TPR_THRESHOLD will be likely written as zero, but the processor will
> > never use it anyway. It's just a small optimization because
> > nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW) will almost always be true.
>
> Theoretically, you are right. But we should not expect all VMMs
> follow it. It is not worth to violate the SDM just for saving two or
> three instructions' cost.
Yes, you do need an "if (cpu_has_vmx_tpr_shadow())" around the
vmcs_write32. But still, checking nested_cpu_has is not strictly
necessary. Right now they both are a single AND, but I have plans to
change all of the cpu_has_*() checks to static keys.
Paolo
next prev parent reply other threads:[~2014-08-01 6:35 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-30 12:04 [PATCH] KVM: nVMX: nested TPR shadow/threshold emulation Wanpeng Li
2014-07-30 15:20 ` Paolo Bonzini
2014-07-31 8:03 ` Wanpeng Li
2014-07-31 9:25 ` Paolo Bonzini
2014-08-01 0:57 ` Zhang, Yang Z
2014-08-01 6:35 ` Paolo Bonzini [this message]
2014-08-01 6:44 ` Zhang, Yang Z
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