On 05/24/2010 04:36 PM, Avi Kivity wrote:
may be simplified if we move xcr0 reload back to guest entry (... :)
but make it lazy:
save_host_state: nothing
set cr4.osxsave: nothing
clear cr4.osxsave: nothing
guest entry: if (gcr4.osxsave && !guest_xcr0_loaded) {
guest_xcr0_loaded = true, load gxcr0 }
load_host_state: if (guest_xcr0_loaded) { guest_xcr0_loaded = false;
load host xcr0 }
fpu switching: if (guest_xcr0_loaded) { guest_xcr0_loaded = false;
load host xcr0 }, do fpu stuff
So we delay xcr0 reload as late as possible for both entry and exit.
btw, this is similar to how we switch the fpu itself:
if-needed-and-not-already-loaded on guest entry, if-loaded on vcpu_put.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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