v5.15-rc7 AMD no kernel dump, spews "scsi_dma_map failed: request for 36 bytes!"

[Marshall Midden <marshallmidden@gmail.com>]

v5.15-rc7 AMD no kernel dump, spews "scsi_dma_map failed: request for 36 bytes!"

With v5.15-rc (1 through 7), AMD processor kernel crash dumps do not occur,
instead spews:
        "scsci_dma_map failed: request for 36 bytes!"
Works on Intel machines, and in v5.14.0 (and v5.14.14) - as well as previous
kernels (down to v5.3.x.)
git bisect torvalds repository shows: dabb16f67215918c48cf3ff1fc4bc36ca421da2b
Reverse patch to tag v5.15-rc7 allows kernel crash dumps to occur/happen.

Extra details in github repository:
    https://github.com/marshallmidden/m4.git
    Directory AMD-cdrash-2021-10-27
        Z.config.2021-10-27_10-27-15
        Z.dabb16f67215918c48cf3ff1fc4bc36ca421da2b
        Z.df-fstab
        Z.dmesg.2021-10-27_10-26-34
        Z.lspci-vmmD.2021-10-27_10-29-58
        rpviewer(5).png

Reproduce via:
    echo c > /proc/sysrq-trigger

git bisect of linux from torvalds repository shows:
    commit dabb16f67215918c48cf3ff1fc4bc36ca421da2b
    Author: Logan Gunthorpe <logang@deltatee.com>
    Date:   Thu Jul 29 14:15:22 2021 -0600

    iommu/dma: return error code from iommu_dma_map_sg()

    Return appropriate error codes EINVAL or ENOMEM from
    iommup_dma_map_sg(). If lower level code returns ENOMEM, then we
    return it, other errors are coalesced into EINVAL.

    iommu_dma_map_sg_swiotlb() returns -EIO as its an unknown error
    from a call that returns DMA_MAPPING_ERROR.

    Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
    Cc: Joerg Roedel <joro@8bytes.org>
    Cc: Will Deacon <will@kernel.org>
    Signed-off-by: Christoph Hellwig <hch@lst.de>
------------------------------------------------------------------------------
[root@parsec torvalds-linux]# awk -f scripts/ver_linux
    Linux parsec 5.15.0-rc4+ #22 SMP Tue Oct 26 18:50:50 CDT 2021
x86_64 x86_64 x86_64 GNU/Linux

    GNU C                       11.1.0
    GNU Make                    3.82
    Binutils                    2.36.1
    Util-linux                  2.23.2
    Mount                       2.23.2
    Module-init-tools           20
    E2fsprogs                   1.42.9
    Xfsprogs                    4.5.0
    Quota-tools                 4.01
    Nfs-utils                   1.3.0
    Bison                       3.0.4
    Flex                        2.5.37
    Linux C++ Library           6.0.19
    Linux C Library             2.17
    Dynamic linker (ldd)        2.17
    Procps                      3.3.10
    Net-tools                   2.10
    Kbd                         1.15.5
    Console-tools               1.15.5
    Sh-utils                    8.22
    Udev                        219
    Modules Loaded              iscsi_target_mod qla2xxx
target_core_file target_core_iblock target_core_mod target_core_pscsi
tcm_fc tcm_loop tcm_qla2xxx

[root@parsec torvalds-linux]# perl scripts/get_maintainer.pl -f
drivers/iommu/dma-iommu.c
    Joerg Roedel <joro@8bytes.org> (maintainer:IOMMU DRIVERS)
    Will Deacon <will@kernel.org> (maintainer:IOMMU DRIVERS)
    iommu@lists.linux-foundation.org (open list:IOMMU DRIVERS)
    linux-kernel@vger.kernel.org (open list)
------------------------------------------------------------------------------
commit dabb16f67215918c48cf3ff1fc4bc36ca421da2b
Author: Logan Gunthorpe <logang@deltatee.com>
Date:   Thu Jul 29 14:15:22 2021 -0600

    iommu/dma: return error code from iommu_dma_map_sg()

    Return appropriate error codes EINVAL or ENOMEM from
    iommup_dma_map_sg(). If lower level code returns ENOMEM, then we
    return it, other errors are coalesced into EINVAL.

    iommu_dma_map_sg_swiotlb() returns -EIO as its an unknown error
    from a call that returns DMA_MAPPING_ERROR.

    Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
    Cc: Joerg Roedel <joro@8bytes.org>
    Cc: Will Deacon <will@kernel.org>
    Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 98ba927..168434c 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -972,7 +972,7 @@ static int iommu_dma_map_sg_swiotlb(struct device
*dev, struct scatterlist *sg,

 out_unmap:
        iommu_dma_unmap_sg_swiotlb(dev, sg, i, dir, attrs |
DMA_ATTR_SKIP_CPU_SYNC);
-       return 0;
+       return -EIO;
 }

 /*
@@ -993,11 +993,13 @@ static int iommu_dma_map_sg(struct device *dev,
struct scatterlist *sg,
        dma_addr_t iova;
        size_t iova_len = 0;
        unsigned long mask = dma_get_seg_boundary(dev);
+       ssize_t ret;
        int i;

-       if (static_branch_unlikely(&iommu_deferred_attach_enabled) &&
-           iommu_deferred_attach(dev, domain))
-               return 0;
+       if (static_branch_unlikely(&iommu_deferred_attach_enabled)) {
+               ret = iommu_deferred_attach(dev, domain);
+               goto out;
+       }

        if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
                iommu_dma_sync_sg_for_device(dev, sg, nents, dir);
@@ -1045,14 +1047,17 @@ static int iommu_dma_map_sg(struct device
*dev, struct scatterlist *sg,
        }

        iova = iommu_dma_alloc_iova(domain, iova_len, dma_get_mask(dev), dev);
-       if (!iova)
+       if (!iova) {
+               ret = -ENOMEM;
                goto out_restore_sg;
+       }

        /*
         * We'll leave any physical concatenation to the IOMMU driver's
         * implementation - it knows better than we do.
         */
-       if (iommu_map_sg_atomic(domain, iova, sg, nents, prot) < iova_len)
+       ret = iommu_map_sg_atomic(domain, iova, sg, nents, prot);
+       if (ret < iova_len)
                goto out_free_iova;

        return __finalise_sg(dev, sg, nents, iova);
@@ -1061,7 +1066,10 @@ static int iommu_dma_map_sg(struct device *dev,
struct scatterlist *sg,
        iommu_dma_free_iova(cookie, iova, iova_len, NULL);
 out_restore_sg:
        __invalidate_sg(sg, nents);
-       return 0;
+out:
+       if (ret != -ENOMEM)
+               return -EINVAL;
+       return ret;
 }

  static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg,