Re: [PATCH v3 10/16] x86/virt/tdx: Drop the outdated requirement that TDX be enabled in IRQ context

[Huang, Kai]

On Tue, 2026-02-17 at 07:25 -0800, Sean Christopherson wrote:
> On Tue, Feb 17, 2026, Kai Huang wrote:
> > On Fri, 2026-02-13 at 17:26 -0800, Sean Christopherson wrote:
> > > Remove TDX's outdated requirement that per-CPU enabling be done via IPI
> > > function call, which was a stale artifact leftover from early versions of
> > > the TDX enablement series.  The requirement that IRQs be disabled should
> > > have been dropped as part of the revamped series that relied on a the KVM
> > > rework to enable VMX at module load.
> > > 
> > > In other words, the kernel's "requirement" was never a requirement at all,
> > > but instead a reflection of how KVM enabled VMX (via IPI callback) when
> > > the TDX subsystem code was merged.
> > > 
> > > Note, accessing per-CPU information is safe even without disabling IRQs,
> > > as tdx_online_cpu() is invoked via a cpuhp callback, i.e. from a per-CPU
> > > thread.
> > > 
> > > Link: https://lore.kernel.org/all/ZyJOiPQnBz31qLZ7@xxxxxxxxxx
> > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > > 
> > 
> > Hi Sean,
> > 
> > The first call of tdx_cpu_enable() will also call into
> > try_init_module_global() (in order to do TDH_SYS_INIT), which also has a
> > lockdep_assert_irqs_disabled() + a raw spinlock to make sure TDH_SYS_INIT is
> > only called once when tdx_cpu_enable() are called from IRQ disabled context.
> > 
> > This patch only changes tdx_cpu_enable() but doesn't change
> > try_init_module_global(), thus the first call of tdx_cpu_enable() will still
> > trigger the lockdep_assert_irqs_disabled() failure warning.
> > 
> > I've tried this series on my local and I did see such WARNING during
> > boot[*].  We need to fix that too.
> > 
> > But hmm, Chao's "Runtime TDX module update" series actually needs to call
> > tdx_cpu_enable() when IRQ disabled, IIUC, since it is called via
> > stop_machine_cpuslocked():
> > 
> > https://lore.kernel.org/kvm/20260212143606.534586-18-chao.gao@xxxxxxxxx/
> > 
> > Maybe we can just keep tdx_cpu_enabled() as-is?
> 
> Can't we simply delete the lockdep assert there as well?  It should be totally
> fine to have a function that can be called from task or IRQ context, so long as
> the function is prepared for that possibility.  I.e. just because it _can_ be
> called from IRQ context doesn't mean it _must_ be called from IRQ context.
> 
> E.g. as a fixup

Yeah we can.  LGTM.