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 13:56, 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. So,
> on a 64 bit machine, if the driver set's the DMA mask to 32 bit then
> SWIOTLB's bounce buffer comes into picture during IOs. Since these
> bounce buffers are limited in size and hence we observe the IO hang if
> the large IOs are issued.
>
> I am not sure whether this API's return value is correct or not in the
> Xen environment. If it is correct then I have to modify the driver to
> not use this API and directly set the DMA mask to 64 bit if the system
> is a 64bit machine.
Please recheck the backported patch in 5.10.y. It is _wrong_. The backport
has:

--- a/drivers/scsi/mpt3sas/mpt3sas_base.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_base.c
@@ -2993,7 +2993,7 @@ _base_config_dma_addressing(struct MPT3SAS_ADAPTER *ioc, 
struct pci_dev *pdev)
        if (ioc->is_mcpu_endpoint ||
            sizeof(dma_addr_t) == 4 || ioc->use_32bit_dma ||
-           dma_get_required_mask(&pdev->dev) <= 32)
+           dma_get_required_mask(&pdev->dev) <= DMA_BIT_MASK(32))
                ioc->dma_mask = 32;
        /* Set 63 bit DMA mask for all SAS3 and SAS35 controllers */
        else if (ioc->hba_mpi_version_belonged > MPI2_VERSION)

While the upstream patch has:

+       if (ioc->is_mcpu_endpoint || sizeof(dma_addr_t) == 4 ||
+           dma_get_required_mask(&pdev->dev) <= 32) {
                ioc->dma_mask = 32;
+               coherent_dma_mask = dma_mask = DMA_BIT_MASK(32);


Juergen

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