On 02/21/2010 02:41 PM, Joerg Roedel wrote:
On Sun, Feb 21, 2010 at 02:24:02PM +0200, Avi Kivity wrote:
On 02/21/2010 02:10 PM, Joerg Roedel wrote:
On Sat, Feb 20, 2010 at 01:26:49PM -1000, Zachary Amsden wrote:
The infrastructure is already there to import / export and migrate MSR
settings. MSRs are also 64-bit, and hold "model-specific" settings, so
if you don't mind thinking of the nested feature as a model-specific
feature of the KVM-SVM CPU, it's even somewhat well defined in terms of
the architecture.
There is a lot of additional state to migrate if the vcpu is running
nested. To be architecturally correct you need to transfer 6kb of data
through MSRs only for the msr permission bitmap.
The msr permission bitmap is in guest memory, so it is already migrated.
This will work almost always but its not architecturally correct
because the memory contents may have changed since the last vmrun
instruction. On the other hand we already have this problem with the
current nested msr intercept handling...
So, if some other cpu (or the guest itself, with appropriate
permissions) modifies the msr permission bitmap, svm will not notice
this? svm loads the bitmap during entry?
The rest comes down to
the nested intercept masks
These are in the vmcb, which is in guest memory.
Same as with the MSR permission map here.
Yes (as with the msr permission bitmap pointers).
It is doable but I still think its
complicated to get this right. The simplest approach would be to
disallow migration when the vcpu is running in guest mode.
Agree, though I dislike the need to introduce a "force vmexit" ioctl.
Yes, this has possible issues too. If we reconstruct the nested state from
the nested vmcb there is not much state left which needs migration. But
we should keep in mind that this is not how real hardware works.
I don't think you can tell, unless the host cpu modifying the vmcb is
synchronized with the guest (or the guest modifies its own vmcb). But
this is all academic.
--
error compiling committee.c: too many arguments to function
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