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SubjectRe: [RFC v2 08/32] x86/traps: Add #VE support for TDX guest
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On 6/8/2021 10:53 AM, Dave Hansen wrote:
> 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?

I believe neither does mmio/msr normally (except maybe ftrace+tp_printk,
but that will likely work because it shouldn't recurse more than once
due to ftrace's reentry protection)

-Andi

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