++ CC'd
On Mon, Nov 6, 2023 at 6:02 PM Joe Lopez <jlo...@gmail.com> wrote: > From: joelopez333 <jlo...@gmail.com> > > REF:https://edk2.groups.io/g/devel/topic/102310377#110456 > > Problem Report: > > On AARCH64, there is no ordering guarantee between configuration > space (ECAM) writes and memory space reads (MMIO). ARM AMBA CHI > only guarantees ordering for reads and writes within a single address > region, > however, on some systems MMIO and ECAM may be split into separate > address regions. > > A problem may arise when an ECAM write is issued a completion before a > subsequent > MMIO read is issued and receives a completion. > > For example, a typical PCI software flow is the following: > > 1. ECAM write to device command register to enable memory space > 2. MMIO read from device memory space for which access was enabled > in step 1. > > There is no guarantee that step 2. will not begin before the > completion of step 1. > on systems where ECAM/MMIO are specified as separate address regions, > even > if both spaces have the memory attributes device-nGnRnE. > > Fix: > > - Add a read after the final PCI Configuration space write > in RootBridgeIoPciAccess. > > - When configuration space is strongly ordered, this ensures > that program execution cannot continue until the completion > is received for the previous Cfg-Write, which may have side-effects. > > - Risk of reading a "write-only" register and causing a CA which > leaves the device > unresponsive. The expectation based on the PCI Base Spec v6.1 > section 7.4 is that > all PCI Spec-defined registers will be readable, however, there may > exist > design-specific registers that fall into this category. > > Cc: Leif Lindholm <quic_llind...@quicinc.com> > Cc: Ard Biesheuvel <ardb+tianoc...@kernel.org> > Cc: Sami Mujawar <sami.muja...@arm.com> > Cc: Jian J Wang <jian.j.w...@intel.com> > Cc: Liming Gao <gaolim...@byosoft.com.cn> > Cc: Hao A Wu <hao.a...@intel.com> > Cc: Ray Ni <ray...@intel.com> > Cc: Pedro Falcato <pedro.falc...@gmail.com> > Cc: Michael Brown <mc...@ipxe.org> > Signed-off-by: Joe Lopez <jlot...@gmail.com> > --- > MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c > b/MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c > index 157a0ada80..c2dc2018d6 100644 > --- a/MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c > +++ b/MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c > @@ -1238,6 +1238,14 @@ RootBridgeIoPciAccess ( > } > } > > + // > + // Perform readback after write to confirm completion was received for > the last write > + // before subsequent memory operations can be issued. > + // > + if (!Read) { > + PciSegmentRead8 (Address - InStride); > + } > + > return EFI_SUCCESS; > } > > -- > 2.25.1 > > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#110874): https://edk2.groups.io/g/devel/message/110874 Mute This Topic: https://groups.io/mt/102435564/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
