Re: PciBusDxe: PCI-Express bug with dynamic PcdPciExpressBaseAddress

["Ni, Ruiyu" <ruiyu.ni@intel.com>]

Mike,
Do you think that maybe just raising to TPL_NOTIFY is enough for PCI BAR probing?
Though the timer interrupt still triggers, all callbacks are suspended in TPL_NOTIFY.

Thanks,
Ray

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Nikita
> Leshenko
> Sent: Friday, September 7, 2018 3:09 AM
> To: edk2-devel@lists.01.org
> Cc: Liran Alon <liran.alon@oracle.com>
> Subject: [edk2] PciBusDxe: PCI-Express bug with dynamic
> PcdPciExpressBaseAddress
> 
> Hi,
> 
> We ran into a bug in EDK2 relating to PCI-Express in PciBusDxe. Here's the flow
> of the bug:
> 
> 1. PciBusDxe/PciEnumeratorSupport.c: Function BarExisted probes a BAR. It
> raises
>    TPL to TPL_HIGH_LEVEL to avoid timer interrupts while probing the BAR and
>    calls PciIo->Pci.Write.
> 2. BasePciExpressLib/PciExpressLib.c: The write reaches PciExpressWrite32,
> which
>    calls GetPciExpressBaseAddress.
> 3. GetPciExpressBaseAddress retrieves the address from
> PcdPciExpressBaseAddress.
> 4. Reading the PCD calls DxePcdGet64 -> GetWorker ->
>    EfiAcquireLock(&mPcdDatabaseLock), which is at TPL_NOTIFY level. This
> crashes
>    the firmware because step 1 raised the TPL to TPL_HIGH_LEVEL.
> 
> This doesn't happen when PcdPciExpressBaseAddress is fixed at build (because
> then the read is optimized to a static global variable), but when the PCD is
> dynamic PCI-Express is broken.
> 
> Does anybody have a suggestion for fixing it?
> 
> Options we thought about:
> - Change mPcdDatabaseLock.Tpl to TPL_HIGH_LEVEL
> - Don't use a PCD for the base address, put it in a static global variable and
>   create functions to set and retrieve it.
> 
> Thanks,
> Nikita
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