[edk2-devel][PATCH v2 0/2] Add Volatile Keyword to NvmExpress Passthru CQs

[Oliver Smith-Denny]

NVMe CQs are hardware queues mapped to EFI memory.
In the NVMExpress Passthru implementations in PEI and DXE,
it has been observed that NVMe CQs are not marked
volatile, meaning the compiler has significant leeway
to optimize accesses to these structures.

This led to an issue where the passthru driver waited
for a timeout period for an NVMe CQ to mark that it was
finished with a transaction, but the compiler had
optimized away the read to the actual HW mapped memory,
so the transaction had completed but the timeout continued.

Marking the CQs as volatile fixes this issue as the reads
happen to the actual HW.

Personal GitHub PR: https://github.com/tianocore/edk2/pull/4320
Github branch: https://github.com/os-d/edk2/tree/osde/volatile_cq_v2

Changes v1 => v2:
=================
- Remove volatile keyword from SQ

Cc: Hao A Wu <hao.a.wu at intel.com>
Cc: Ray Ni <ray.ni at intel.com>
Cc: Jian J Wang <jian.j.wang at intel.com>
Cc: Liming Gao <gaoliming at byosoft.com.cn>
Cc: Michael Kubacki <mikuback at linux.microsoft.com>
Cc: Sean Brogan <sean.brogan at microsoft.com>


Oliver Smith-Denny (2):
  Add the volatile keyword to NvmExpressDxe's Passthru CQ
  Add volatile keyword to NvmExpressPei's Passthru CQ

 MdeModulePkg/Bus/Pci/NvmExpressDxe/NvmExpressPassthru.c    | 6 +++---
 MdeModulePkg/Bus/Pci/NvmExpressPei/NvmExpressPeiPassThru.c | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

-- 
2.40.0



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