From 8523b54b7410c1beee60615bad5b674568bc8eeb Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= Date: Tue, 30 Jun 2026 14:58:58 +0200 Subject: [PATCH] iommu/amd-vi: do not zero IOMMU MMIO region MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Attempting to memset the whole IOMMU MMIO region to zero is dangerous to say the least. We don't know which 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 Monné Reviewed-by: Andrew Cooper master commit: bdb30883f3528676f8b736e4ec0e475914289993 master date: 2026-05-06 18:56:59 +0200 --- 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/passthrough/amd/iommu_init.c index ac897d7302..552d439f44 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, u8 mask) return iommu->ht_flags & mask; } -static int __init map_iommu_mmio_region(struct amd_iommu *iommu) -{ - iommu->mmio_base = 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 ) @@ -1369,11 +1357,14 @@ static int __init amd_iommu_prepare_one(struct amd_iommu *iommu) { int rc = alloc_ivrs_mappings(iommu->seg); - if ( !rc ) - rc = map_iommu_mmio_region(iommu); if ( rc ) return rc; + iommu->mmio_base = ioremap(iommu->mmio_base_phys, + IOMMU_MMIO_REGION_LENGTH); + if ( !iommu->mmio_base ) + return -ENOMEM; + get_iommu_features(iommu); /* @@ -1383,6 +1374,20 @@ static int __init amd_iommu_prepare_one(struct amd_iommu *iommu) if ( amd_iommu_max_paging_mode < amd_iommu_min_paging_mode ) return -ERANGE; + /* + * Check whether the IOMMU is already enabled and unconditionally disable + * it (zero the control register) ahead of Xen setup. Needs to be + * revisited to support Preboot DMA Protection. + */ + iommu->ctrl.raw = 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", + &PCI_SBDF(iommu->seg, iommu->bdf), iommu->ctrl.raw); + + iommu->ctrl.raw = 0; + writeq(0, iommu->mmio_base + IOMMU_CONTROL_MMIO_OFFSET); + return 0; }