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

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Date:   Mon, 24 Oct 2022 14:55:51 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
        Bart Van Assche <bvanassche@....org>
Cc:     Salvatore Bonaccorso <carnil@...ian.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        sathya.prakash@...adcom.com, suganath-prabu.subramani@...adcom.com,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        MPT-FusionLinux.pdl@...adcom.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        adi@...egisch.at
Subject: Re: Report in downstream Debian: mpt3sas broken with xen dom0 with
 update to 5.10.149 in 5.10.y.

On 24.10.22 13:56, Sreekanth Reddy wrote:
> On Sun, Oct 23, 2022 at 6:57 AM Bart Van Assche <bvanassche@....org> 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@eldamar.lan/.
> 
> 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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