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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Tao Xu <tao3.xu@intel.com>
Cc: pbonzini@redhat.com, rkrcmar@redhat.com, corbet@lwn.net,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	hpa@zytor.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	fenghua.yu@intel.com, xiaoyao.li@linux.intel.com,
	jingqi.liu@intel.com
Subject: Re: [PATCH v7 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL
Date: Mon, 15 Jul 2019 07:16:36 -0700
Message-ID: <20190715141636.GB442@linux.intel.com> (raw)
In-Reply-To: <8ed3cec5-8ba9-b2ed-f0e4-eefb0a988bc8@intel.com>

On Mon, Jul 15, 2019 at 09:22:14AM +0800, Tao Xu wrote:
> On 7/12/2019 11:52 PM, Sean Christopherson wrote:
> >The SDM only defines bits 31:0, and the kernel uses a u32 to cache its
> >value.  I assume bits 63:32 are reserved?  I'm guessing we also need an
> >SDM update...
> >
> 
> The SDM define IA32_UMWAIT_CONTROL is a 32bit MSR. So need me to set 63:32
> reserved?

Huh, I didn't realize the SDM allows 32 bit MSRs, I assumed all bits
needed to be explicitly defined even if the underlying implementation only
tracked 32 bits.

RDMSR:

  If fewer than 64 bits are implemented in the MSR being read, the values
  return in EDX:EAX in unimplemented bit locations are undefined.

WRMSR:

  Undefined or reserved bits in an MSR should be set to values previously
  read.

From KVM's perspective, bits 63:32 should be treated as reserved-to-zero.
This also means that struct vcpu_vmx can track a u32 instead of a u64
for msr_ia32_umwait_control.

  reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-12  8:29 [PATCH v7 0/3] KVM: x86: Enable user wait instructions Tao Xu
2019-07-12  8:29 ` [PATCH v7 1/3] KVM: x86: add support for " Tao Xu
2019-07-12 15:13   ` Sean Christopherson
2019-07-15  1:11     ` Tao Xu
2019-07-12  8:29 ` [PATCH v7 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL Tao Xu
2019-07-12 15:52   ` Sean Christopherson
2019-07-15  1:22     ` Tao Xu
2019-07-15 14:16       ` Sean Christopherson [this message]
2019-07-16 16:03   ` Eduardo Habkost
2019-07-17  1:17     ` Tao Xu
2019-07-17  2:03       ` Tao Xu
2019-07-12  8:29 ` [PATCH v7 3/3] KVM: vmx: handle vm-exit for UMWAIT and TPAUSE Tao Xu
2019-07-12 16:03   ` Sean Christopherson
2019-07-13 14:22     ` Tao Xu

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