| Date | Thu, 23 Jul 2020 16:41:11 -0700 | From | Sean Christopherson <> | Subject | Re: [patch V5 08/15] x86/entry: Move user return notifier out of loop |
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On Thu, Jul 23, 2020 at 12:00:02AM +0200, Thomas Gleixner wrote: > From: Thomas Gleixner <tglx@linutronix.de> > > Guests and user space share certain MSRs. KVM sets these MSRs to guest > values once and does not set them back to user space values on every VM > exit to spare the costly MSR operations. > > User return notifiers ensure that these MSRs are set back to the correct > values before returning to user space in exit_to_usermode_loop(). > > There is no reason to evaluate the TIF flag indicating that user return > notifiers need to be invoked in the loop. The important point is that they > are invoked before returning to user space. > > Move the invocation out of the loop into the section which does the last > preperatory steps before returning to user space. That section is not > preemptible and runs with interrupts disabled until the actual return. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-and-tested-by: Sean Christopherson <sean.j.christopherson@intel.com>
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