From: Sheng Yang <sheng@linux.intel.com>
To: kvm@vger.kernel.org
Cc: Kurt Kiefer <kekiefer@gmail.com>
Subject: Re: Question about guest MSR loading/saving (Intel)
Date: Tue, 2 Feb 2010 10:53:23 +0800 [thread overview]
Message-ID: <201002021053.23730.sheng@linux.intel.com> (raw)
In-Reply-To: <0910BB5A-E4FA-4085-978E-D6374A1376B7@gmail.com>
On Tuesday 02 February 2010 09:57:08 Kurt Kiefer wrote:
> Hi all,
>
> This is a vague/general question. For some background: I have a reason
> (control of IA32_PERF_GLOBAL_CTRL) for loading/saving MSRs on VM-entry/
> exit. To get this to work correctly, I made changes to use the
> conventional VMX MSR load areas of the VMCS for this particular MSR.
> Works great.
>
> Is there a particular reason why MSRs are currently loaded/saved
> through KVM's unconventional facilities (vmx.c:save_msrs(),
> vmx.c:load_msrs()), rather than through VM entry/exit MSR load regions
> in the VMCS? I see that only long mode guests on x86_64 are effected
> by this.
>
> Any insight could be useful. Do you think MSR loading via VMCS would
> be faster? Are there downsides to doing it one way or the other?
>
Because not all MSRs are supported for automatically save/load when VMX
transition happened. You used IA32_PERF_GLOBAL_CTRL is supported. But not the
ones saved in save_msrs().
--
regards
Yang, Sheng
next prev parent reply other threads:[~2010-02-02 2:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-02 1:57 Question about guest MSR loading/saving (Intel) Kurt Kiefer
2010-02-02 2:53 ` Sheng Yang [this message]
2010-02-04 19:12 ` Avi Kivity
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