(+Ard)
On 09/06/18 21:08, Nikita Leshenko wrote:
> 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.
In the ArmVirtPkg platforms, we also set "PcdPciExpressBaseAddress"
dynamically. And, we implemented your second option above; see:
ArmVirtPkg/Library/BaseCachingPciExpressLib/
Relevant commits:
- ad3359eb43a9 ("ArmVirtualizationPkg: clone BasePciExpressLib, cache
PCIe config base", 2015-02-23)
- a06d0bb58eb9 ("ArmVirtPkg/BaseCachingPciExpressLib: depend on
PciPcdProducerLib", 2016-04-12)
(In fact, commit ad3359eb43a9 documents the exact issue you report here.)
Thanks
Laszlo
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