tree d2f4e83b00ecfc8d744c8f8af5510bca5a8185cc
parent 5315c716b69f47e1751d09e16c7bd5b559419531
author Paolo Bonzini <pbonzini@redhat.com> 1392975147 +0100
committer Paolo Bonzini <pbonzini@redhat.com> 1394531164 +0100

KVM: svm: Allow the guest to run with dirty debug registers

When not running in guest-debug mode (i.e. the guest controls the debug
registers, having to take an exit for each DR access is a waste of time.
If the guest gets into a state where each context switch causes DR to be
saved and restored, this can take away as much as 40% of the execution
time from the guest.

If the guest is running with vcpu->arch.db == vcpu->arch.eff_db, we
can let it write freely to the debug registers and reload them on the
next exit.  We still need to exit on the first access, so that the
KVM_DEBUGREG_WONT_EXIT flag is set in switch_db_regs; after that, further
accesses to the debug registers will not cause a vmexit.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>