Re: [RFC v2 08/32] x86/traps: Add #VE support for TDX guest

[Dave Hansen]

On 6/8/21 10:48 AM, Sean Christopherson wrote:
> On Tue, Jun 08, 2021, Dave Hansen wrote:
>> On 4/26/21 11:01 AM, Kuppuswamy Sathyanarayanan wrote:
>>> +#ifdef CONFIG_INTEL_TDX_GUEST
>>> +DEFINE_IDTENTRY(exc_virtualization_exception)
>>> +{
>>> +	struct ve_info ve;
>>> +	int ret;
>>> +
>>> +	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
>>> +
>>> +	/*
>>> +	 * Consume #VE info before re-enabling interrupts. It will be
>>> +	 * re-enabled after executing the TDGETVEINFO TDCALL.
>>> +	 */
>>> +	ret = tdg_get_ve_info(&ve);
>> Is it safe to have *anything* before the tdg_get_ve_info()?  For
>> instance, say that RCU_LOCKDEP_WARN() triggers.  Will anything in there
>> do MMIO?
> I doubt it's safe, anything that's doing printing has the potential to trigger
> #VE.  Even if we can prove it's safe for all possible paths, I can't think of a
> reason to allow anything that's not absolutely necessary before retrieving the
> #VE info.

What about tracing?  Can I plop a kprobe in here or turn on ftrace?