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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,
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.


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


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

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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