lkml.org 
[lkml]   [2010]   [May]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] Add Documentation/kvm/msr.txt
    On Thu, May 27, 2010 at 10:13:12AM -1000, Zachary Amsden wrote:
    > On 05/27/2010 06:02 AM, Glauber Costa wrote:
    > >On Thu, May 27, 2010 at 11:15:43AM +0300, Avi Kivity wrote:
    > >>On 05/26/2010 09:04 PM, Glauber Costa wrote:
    > >>>This patch adds a file that documents the usage of KVM-specific
    > >>>MSRs.
    > >>>
    > >>Looks good. A few comments:
    > >>
    > >>>+
    > >>>+Custom MSR list
    > >>>+--------
    > >>>+
    > >>>+The current supported Custom MSR list is:
    > >>>+
    > >>>+MSR_KVM_WALL_CLOCK: 0x11
    > >>>+
    > >>>+ data: physical address of a memory area.
    > >>Which must be in guest RAM (i.e., don't point it somewhere random
    > >>and expect the hypervisor to allocate it for you).
    > >>
    > >>Must be aligned to 4 bytes (we don't enforce it though).
    > >I don't see the reason for it.
    > >
    > >If this is a requirement, our own implementation
    > >is failing to meet it.
    >
    > It's so the atomic write actually is atomic.
    Which atomic write? This is the wallclock, we do no atomic writes for
    querying it. Not to confuse with system time (the other msr).

    > Stating a 4 -byte
    > alignment requirement prevents the wall clock from crossing a page
    > boundary.

    Yes, but why require it?

    reading the wallclock is not a hot path for anybody, is usually done
    just once, and crossing a page boundary here does not pose any correctness
    issue.


    \
     
     \ /
      Last update: 2010-05-27 22:39    [W:0.045 / U:0.104 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site