Re: Report in downstream Debian: mpt3sas broken with xen dom0 with update to 5.10.149 in 5.10.y.

[Juergen Gross <jgross@xxxxxxxx>]

On 24.10.22 14:51, James Bottomley wrote:
> On Mon, 2022-10-24 at 17:26 +0530, Sreekanth Reddy wrote:
> > On Sun, Oct 23, 2022 at 6:57 AM Bart Van Assche <bvanassche@xxxxxxx>
> > wrote:
> > > On 10/21/22 02:22, Salvatore Bonaccorso wrote:
> > > > We got the following report in Debian after an update from
> > > > 5.10.140 to
> > > > the current 5.10.149. Full quoting below (from
> > > > https://bugs.debian.org/1022126). Does this ring some bell about
> > > > known
> > > > regressions?
> > > Only three mpt3sas changes are new in v5.10.149 compared to
> > > v5.10.140:
> > > $ git log --format=oneline v5.10.140..v5.10.149
> > > 2b9aba0c5d58e141e32bb1bb4c7cd91d19f075b8 scsi: mpt3sas: Fix return
> > > value check of dma_get_required_mask()
> > > e7fafef9830c4a01e60f76e3860a9bef0262378d scsi: mpt3sas: Force PCIe
> > > scatterlist allocations to be within same 4 GB region
> > > ea10a652ad2ae2cf3eced6f632a5c98f26727057 scsi: mpt3sas: Fix use-
> > > after-free warning
> > >
> > > Sreekanth and Suganath, can you help with bisecting this issue? For
> > > the
> > > full report, see also
> > > https://lore.kernel.org/linux-scsi/Y1JkuKTjVYrOWbvm@xxxxxxxxxxx/.
> > This issue is getting observed after having the below patch changes,
> > 2b9aba0c5d58e141e32bb1bb4c7cd91d19f075b8 scsi: mpt3sas: Fix return
> > value check of dma_get_required_mask()
> >
> > What is happening is that on Xen hypervisor, this
> > dma_get_required_mask() API always returns a 32 bit DMA mask. I.e. It
> > says that the minimum DMA mask required to access the host memory is
> > 32 bit and hence mpt3sas driver is setting the DMA mask to 32bit.
> This sounds entirely correct because the VM is booted with (from the
> original debian bug report):
>
> dom0_mem=4096M,max:4096M dom0_max_vcpus=4 dom0_vcpus_pin
>    ucode=scan xpti=dom0=false,domu=true gnttab_max_frames=128
>
> So it has no memory above 4GB and thus 32 bit addressing is the minimum
> required.  If you boot a machine with >4GB and Xen still returns a 32
> bit mask here, then we have a Xen problem.
Dom0 is (normally) a PV domain, so the physical memory can be still above
4 GB even with dom0_mem set to 4GB.

But please see my other reply to this thread. I think at least one of the
backports is plain wrong.


Juergen

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