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We don't know what registers might be there, nor which values might be safe for those registers. On a forthcoming platform doing the zeroing of the MMIO region does put the IOMMU in a broken state, which is not recoverable by the IOMMU initialization procedure in Xen. Instead just zero the control register, which mimics the current behavior with regards to how the control register is handled, and ensures the IOMU setup is done with the unit disabled. This approach will need revisiting in order to support Preboot DMA Protection. Fold map_iommu_mmio_region() into its only caller, as the function body is just an ioremap() call after the removal of the memset(). Fixes: 0700c962ac2d ("Add AMD IOMMU support into hypervisor") Signed-off-by: Roger Pau Monn=C3=A9 Reviewed-by: Andrew Cooper --- Changes since v2: - Avoid the disable_iommu() dance. - Expand commit message a bit. Changes since v1: - Zero the control register after calling disable_iommu(). - Print a warning message if the IOMMU is handed enabled to Xen from firmware. - Fix commit log grammar issues. --- xen/drivers/passthrough/amd/iommu_init.c | 33 ++++++++++++++---------- 1 file changed, 19 insertions(+), 14 deletions(-) diff --git a/xen/drivers/passthrough/amd/iommu_init.c b/xen/drivers/passthr= ough/amd/iommu_init.c index d77dd8511288..e0c8925c33f7 100644 --- a/xen/drivers/passthrough/amd/iommu_init.c +++ b/xen/drivers/passthrough/amd/iommu_init.c @@ -42,18 +42,6 @@ static bool iommu_has_ht_flag(struct amd_iommu *iommu, u= 8 mask) return iommu->ht_flags & mask; } =20 -static int __init map_iommu_mmio_region(struct amd_iommu *iommu) -{ - iommu->mmio_base =3D ioremap(iommu->mmio_base_phys, - IOMMU_MMIO_REGION_LENGTH); - if ( !iommu->mmio_base ) - return -ENOMEM; - - memset(iommu->mmio_base, 0, IOMMU_MMIO_REGION_LENGTH); - - return 0; -} - static void __init unmap_iommu_mmio_region(struct amd_iommu *iommu) { if ( iommu->mmio_base ) @@ -1367,11 +1355,14 @@ static int __init amd_iommu_prepare_one(struct amd_= iommu *iommu) { int rc =3D alloc_ivrs_mappings(iommu->sbdf.seg); =20 - if ( !rc ) - rc =3D map_iommu_mmio_region(iommu); if ( rc ) return rc; =20 + iommu->mmio_base =3D ioremap(iommu->mmio_base_phys, + IOMMU_MMIO_REGION_LENGTH); + if ( !iommu->mmio_base ) + return -ENOMEM; + get_iommu_features(iommu); =20 /* @@ -1381,6 +1372,20 @@ static int __init amd_iommu_prepare_one(struct amd_i= ommu *iommu) if ( amd_iommu_max_paging_mode < amd_iommu_min_paging_mode ) return -ERANGE; =20 + /* + * Check whether the IOMMU is already enabled and unconditionally disa= ble + * it (zero the control register) ahead of Xen setup. Needs to be + * revisited to support Preboot DMA Protection. + */ + iommu->ctrl.raw =3D readq(iommu->mmio_base + IOMMU_CONTROL_MMIO_OFFSET= ); + if ( iommu->ctrl.iommu_en ) + printk(XENLOG_WARNING + "AMD-Vi: IOMMU %pp enabled by firmware (ctrl %016lx)\n", + &iommu->sbdf, iommu->ctrl.raw); + + iommu->ctrl.raw =3D 0; + writeq(0, iommu->mmio_base + IOMMU_CONTROL_MMIO_OFFSET); + return 0; } =20 --=20 2.53.0