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

[Klaus Jensen]

On Dec  8 12:39, Guenter Roeck wrote:
> On Thu, Dec 08, 2022 at 12:13:55PM -0800, Guenter Roeck wrote:
> > On Thu, Dec 08, 2022 at 10:47:42AM -0800, Guenter Roeck wrote:
> > > > 
> > > > A cq head doorbell mmio is skipped... And it is not the fault of the
> > > > kernel. The kernel is in it's good right to skip the mmio since the cq
> > > > eventidx is not properly updated.
> > > > 
> > > > Adding that and it boots properly on riscv. But I'm perplexed as to why
> > > > this didnt show up on our regularly tested platforms.
> > > > 
> > > > Gonna try to get this in for 7.2!
> > > 
> > > I see another problem with sparc64.
> > > 
> > > [    5.261508] could not locate request for tag 0x0
> > > [    5.261711] nvme nvme0: invalid id 0 completed on queue 1
> > > 
> > > That is seen repeatedly until the request times out. I'll test with
> > > your patch to see if it resolves this problem as well, and will bisect
> > > otherwise.
> > > 
> > The second problem is unrelated to the doorbell problem.
> > It is first seen in qemu v7.1. I'll try to bisect.
> > 
> 
> Unfortunately, the problem observed with sparc64 also bisects to this
> patch. Making things worse, "hw/nvme: fix missing cq eventidx update"
> does not fix it (which is why I initially thought it was unrelated).
> 
> I used the following qemu command line.
> 
> qemu-system-sparc64 -M sun4v -cpu "TI UltraSparc IIi" -m 512 -snapshot \
>     -device nvme,serial=foo,drive=d0,bus=pciB \
>     -drive file=rootfs.ext2,if=none,format=raw,id=d0 \
>     -kernel arch/sparc/boot/image -no-reboot \
>     -append "root=/dev/nvme0n1 console=ttyS0" \
>     -nographic -monitor none
> 

Hi Guenter,

Thank you very much for the detailed reports and I apologize for the
fallout of this.

I think this is related to missing endian conversions when handling the
shadow doorbells. I'm not sure if there is a kernel issue here as well,
because as far as I can tell, the shadow doorbells are updated like so:

  old_value = *dbbuf_db;
  *dbbuf_db = value;

(where `value` is the new head/tail value depending on if this is an sq
or cq).

Keith, is the kernel doing something magically here I am not aware of,
or isn't this missing some cpu_to_le32() / le32_to_cpu() calls as well?

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