Re: [edk2-devel] [PATCH 2/2] MdeModulePkg/DxeCore: Fix stack overflow issue due to nested interrupts

["Michael D Kinney" <michael.d.kinney@intel.com>]

Hi Michael,

Can you provide a pointer to the UEFI Spec statement this breaks?

Thanks,

Mike 

> -----Original Message-----
> From: Michael Brown <mcb30@ipxe.org>
> Sent: Thursday, February 29, 2024 5:23 AM
> To: devel@edk2.groups.io; Ni, Ray <ray.ni@intel.com>
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Liming Gao
> <gaoliming@byosoft.com.cn>; Laszlo Ersek <lersek@redhat.com>; Paolo
> Bonzini <pbonzini@redhat.com>
> Subject: Re: [edk2-devel] [PATCH 2/2] MdeModulePkg/DxeCore: Fix stack
> overflow issue due to nested interrupts
> 
> On 29/02/2024 13:02, Ni, Ray wrote:
> > A ideal solution is to not keep the interrupt disabled when
> > RestoreTPL(TPL_HIGH -> not TPL_HIGH) is executed in the timer
> interrupt
> > context because the interrupt handler will re-enable the interrupt
> with
> > arch specific instructions (e.g.: IRET for x86).
> >
> > The patch introduces mInterruptedTplMask which tells RestoreTPL() if
> > it's called in the interrupt context and whether it should defer
> enabling
> > the interrupt.
> 
> NACK.  This breaks the specification-defined behaviour for
> RestoreTPL().
> 
> What guarantees do we have that there is no code anywhere in the world
> that relies upon RestoreTPL() unconditionally re-enabling interrupts.
> 
> I also find this code substantially harder to follow than
> NestedInterruptTplLib (which does not break any specified behaviour).
> 
> Thanks,
> 
> Michael



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