Re: KVM: x86: Push potential exception error code on task switches

[Gleb Natapov <gleb@redhat.com>]

On Wed, Apr 14, 2010 at 02:11:39PM +0200, Jan Kiszka wrote:
>  static int emulator_do_task_switch(struct x86_emulate_ctxt *ctxt,
> -				    struct x86_emulate_ops *ops,
> -				    u16 tss_selector, int reason)
> +				   struct x86_emulate_ops *ops,
> +				   u16 tss_selector, int reason,
> +				   bool has_error_code, u32 error_code)
>  {
>  	struct desc_struct curr_tss_desc, next_tss_desc;
>  	int ret;
> @@ -2416,12 +2417,23 @@ static int emulator_do_task_switch(struct x86_emulate_ctxt *ctxt,
>  	ops->set_cached_descriptor(&next_tss_desc, VCPU_SREG_TR, ctxt->vcpu);
>  	ops->set_segment_selector(tss_selector, VCPU_SREG_TR, ctxt->vcpu);
>  
> +	if (ret == X86EMUL_CONTINUE && has_error_code) {
It looks like we shouldn't get here if ret != X86EMUL_CONTINUE in the
first place. This check should be done just after call to
task_switch_16/32. Not directly related to your patch, but still...

> @@ -2416,12 +2417,23 @@ static int emulator_do_task_switch(struct
> x86_emulate_ctxt *ctxt,
>       ops->set_cached_descriptor(&next_tss_desc, VCPU_SREG_TR,
>       ctxt->vcpu);
>       ops->set_segment_selector(tss_selector, VCPU_SREG_TR,
>       ctxt->vcpu);
>  
> +     if (ret == X86EMUL_CONTINUE && has_error_code) {
> +             struct decode_cache *c = &ctxt->decode;
> +
> +             c->op_bytes = c->ad_bytes = (next_tss_desc.type & 8) ? 4
> : 2;
> +             c->lock_prefix = 0;
> +             c->src.val = (unsigned long) error_code;
> +             emulate_push(ctxt);
> +             ret = writeback(ctxt, ops);
> +     }
I would move writeback() to emulator_task_switch(). Just make
c->dst.type = OP_NONE if writeback is not needed.

--
			Gleb.