Revert "kvm: x86: optimize dr6 restore" (f9dcf08e) · Commits · 戴 / test

This reverts commit . As Christian Ehrhardt noted: The most common case is that vcpu->arch.dr6 and the host's %dr6 value are not related at all because ->switch_db_regs is zero. To do this all correctly, we must handle the case where the guest leaves an arbitrary unused value in vcpu->arch.dr6 before disabling breakpoints again. However, this means that vcpu->arch.dr6 is not suitable to detect the need for a %dr6 clear. Signed-off-by:

Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/x86.c

+4 −9

Original line number	Diff line number	Diff line
		@@ -3271,15 +3271,10 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
		kvm_x86_ops->vcpu_put(vcpu);
		vcpu->arch.last_host_tsc = rdtsc();
		/*
		* Here dr6 is either zero or, if the guest has run and userspace
		* has not set any breakpoints or watchpoints, it can be set to
		* the guest dr6 (stored in vcpu->arch.dr6). do_debug expects dr6
		* to be cleared after it runs, so clear the host register. However,
		* MOV to DR can be expensive when running nested, omit it if
		* vcpu->arch.dr6 is already zero: in that case, the host dr6 cannot
		* currently be nonzero.
		*/
		if (vcpu->arch.dr6)
		* If userspace has set any breakpoints or watchpoints, dr6 is restored
		* on every vmexit, but if not, we might have a stale dr6 from the
		* guest. do_debug expects dr6 to be cleared after it runs, do the same.
		*/
		set_debugreg(0, 6);
		}

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