Re: [PATCH v3 1/2] hw/nvme: Implement shadow doorbell buffer support

[Guenter Roeck]

Hi,

On Thu, Jun 16, 2022 at 08:34:07PM +0800, Jinhao Fan wrote:
> Implement Doorbel Buffer Config command (Section 5.7 in NVMe Spec 1.3)
> and Shadow Doorbel buffer & EventIdx buffer handling logic (Section 7.13
> in NVMe Spec 1.3). For queues created before the Doorbell Buffer Config
> command, the nvme_dbbuf_config function tries to associate each existing
> SQ and CQ with its Shadow Doorbel buffer and EventIdx buffer address.
> Queues created after the Doorbell Buffer Config command will have the
> doorbell buffers associated with them when they are initialized.
> 
> In nvme_process_sq and nvme_post_cqe, proactively check for Shadow
> Doorbell buffer changes instead of wait for doorbell register changes.
> This reduces the number of MMIOs.
> 
> In nvme_process_db(), update the shadow doorbell buffer value with
> the doorbell register value if it is the admin queue. This is a hack
> since hosts like Linux NVMe driver and SPDK do not use shadow
> doorbell buffer for the admin queue. Copying the doorbell register
> value to the shadow doorbell buffer allows us to support these hosts
> as well as spec-compliant hosts that use shadow doorbell buffer for
> the admin queue.
> 
> Signed-off-by: Jinhao Fan <fanjinhao21s@ict.ac.cn>

I noticed that I can no longer boot Linux kernels from nvme on riscv64
systems. The problem is seen with qemu v7.1 and qemu v7.2-rc4.
The log shows:

[   35.904128] nvme nvme0: I/O 642 (I/O Cmd) QID 1 timeout, aborting
[   35.905000] EXT4-fs (nvme0n1): mounting ext2 file system using the ext4 
subsystem
[   66.623863] nvme nvme0: I/O 643 (I/O Cmd) QID 1 timeout, aborting
[   97.343989] nvme nvme0: Abort status: 0x0
[   97.344355] nvme nvme0: Abort status: 0x0
[   97.344647] nvme nvme0: I/O 7 QID 0 timeout, reset controller
[   97.350568] nvme nvme0: I/O 644 (I/O Cmd) QID 1 timeout, aborting

This is with the mainline Linux kernel (v6.1-rc8).

Bisect points to this patch. Reverting this patch and a number of associated
patches (to fix conflicts) fixes the problem.

06143d8771 Revert "hw/nvme: Implement shadow doorbell buffer support"
acb4443e3a Revert "hw/nvme: Use ioeventfd to handle doorbell updates"
d5fd309feb Revert "hw/nvme: do not enable ioeventfd by default"
1ca1e6c47c Revert "hw/nvme: unregister the event notifier handler on the main 
loop"
2d26abd51e Revert "hw/nvme: skip queue processing if notifier is cleared"
99d411b5a5 Revert "hw/nvme: reenable cqe batching"
2293d3ca6c Revert "hw/nvme: Add trace events for shadow doorbell buffer"

Qemu command line:

qemu-system-riscv64 -M virt -m 512M \
     -kernel arch/riscv/boot/Image -snapshot \
     -device nvme,serial=foo,drive=d0 \
     -drive file=rootfs.ext2,if=none,format=raw,id=d0 \
     -bios default \
     -append "root=/dev/nvme0n1 console=ttyS0,115200 
earlycon=uart8250,mmio,0x10000000,115200" \
     -nographic -monitor none

Guenter