Re: [PATCH] kvm test: Add 32-bit task switch micro-test

[Gleb Natapov <gleb@redhat.com>]

On Wed, Apr 14, 2010 at 04:12:46PM +0200, Jan Kiszka wrote:
> Gleb, you might want to have a look at this test. When using it with my
> 2.6.34 queue (or below or with QEMU), I get the following, expected
> output:
> 
> fault at 8:4002ef, prev task 18, error code 1234
> post fault
> 
> When using it with master + my error-code patch, I get this:
> 
> fault at 8:4002ef, prev task 18, error code 1234
> 
> post fault
> 
> I.e. there is blank line, a repeated 0x0a character after returning from
> the fault handler. I'm suspecting that IO string rework triggers this.
> Instrumentation of the testdev showed that the spurious puts() was
> emitted over the instruction that the fault handler returns to. Any
> ideas?
> 
Yes, handle_task_switch() needlessly exits to userspace without setting
exit reason, so last exit reason is reused (in your test case this is io write).
This patch should fix the problem:


diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bffd049..d080840 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4740,7 +4740,7 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
 	if (ret == X86EMUL_CONTINUE)
 		kvm_x86_ops->set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
 
-	return (ret != X86EMUL_CONTINUE);
+	return (ret == X86EMUL_CONTINUE);
 }
 EXPORT_SYMBOL_GPL(kvm_task_switch);
 
--
			Gleb.