git: 35170408a7b8 - main - AMD IOMMU: fix per-device IOMMU bypass when IR is enabled

The branch main has been updated by jah:

URL: https://cgit.FreeBSD.org/src/commit/?id=35170408a7b86a879d7e2ffb5ddb70fe75951d89

commit 35170408a7b86a879d7e2ffb5ddb70fe75951d89
Author:     Jason A. Harmening <jah@FreeBSD.org>
AuthorDate: 2025-10-20 01:53:08 +0000
Commit:     Jason A. Harmening <jah@FreeBSD.org>
CommitDate: 2025-10-20 21:06:47 +0000

    AMD IOMMU: fix per-device IOMMU bypass when IR is enabled
    
    When interrupt remapping (IR) is enabled, the device table entry
    (DTE) for a given device will likely be initialized by
    amdiommu_ir_find() during MSI configuration.  This function directly
    calls amdiommu_get_ctx_for_dev() with id_mapped=false, which means that
    any attempt to disable DMA remapping for the device (e.g. by setting
    hw.busdma.pciD.B.S.F='bounce' in the loader tunables) will effectively
    be ignored as the paging mode field in the DTE will not be set to
    0 as required for identity mapping.  This will ultimately produce
    an unusable device, because busdma will later observe the bounce
    configuration through iommu_instantiate_ctx() and will employ the
    non-translated 'bounce' busdma methods for the device, while the DTE
    remains configured to enable translation.
    
    Fix this by tweaking iommu_instantiate_ctx() to always return the
    relevant per-device context object even if translation is disabled,
    and adopt it in amdiommu_ir_find() instead of directly calling
    amdiommu_get_ctx_for_dev().
    
    Reviewed by:    kib
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D53209
---
 sys/dev/iommu/busdma_iommu.c | 7 +++++--
 sys/x86/iommu/amd_intrmap.c  | 9 ++++-----
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/sys/dev/iommu/busdma_iommu.c b/sys/dev/iommu/busdma_iommu.c
index 668ccf056463..82f73d469585 100644
--- a/sys/dev/iommu/busdma_iommu.c
+++ b/sys/dev/iommu/busdma_iommu.c
@@ -295,7 +295,6 @@ iommu_instantiate_ctx(struct iommu_unit *unit, device_t dev, bool rmrr)
 		} else {
 			iommu_free_ctx_locked(unit, ctx);
 		}
-		ctx = NULL;
 	}
 	return (ctx);
 }
@@ -303,6 +302,7 @@ iommu_instantiate_ctx(struct iommu_unit *unit, device_t dev, bool rmrr)
 struct iommu_ctx *
 iommu_get_dev_ctx(device_t dev)
 {
+	struct iommu_ctx *ctx;
 	struct iommu_unit *unit;
 
 	unit = iommu_find(dev, bootverbose);
@@ -313,7 +313,10 @@ iommu_get_dev_ctx(device_t dev)
 		return (NULL);
 
 	iommu_unit_pre_instantiate_ctx(unit);
-	return (iommu_instantiate_ctx(unit, dev, false));
+	ctx = iommu_instantiate_ctx(unit, dev, false);
+	if (ctx != NULL && (ctx->flags & IOMMU_CTX_DISABLED) != 0)
+		ctx = NULL;
+	return (ctx);
 }
 
 bus_dma_tag_t
diff --git a/sys/x86/iommu/amd_intrmap.c b/sys/x86/iommu/amd_intrmap.c
index f8900fe0561f..cce4f57ca323 100644
--- a/sys/x86/iommu/amd_intrmap.c
+++ b/sys/x86/iommu/amd_intrmap.c
@@ -223,9 +223,9 @@ static struct amdiommu_ctx *
 amdiommu_ir_find(device_t src, uint16_t *ridp, bool *is_iommu)
 {
 	devclass_t src_class;
-	device_t requester;
 	struct amdiommu_unit *unit;
 	struct amdiommu_ctx *ctx;
+	struct iommu_ctx *ioctx;
 	uint32_t edte;
 	uint16_t rid;
 	uint8_t dte;
@@ -255,10 +255,9 @@ amdiommu_ir_find(device_t src, uint16_t *ridp, bool *is_iommu)
 		error = amdiommu_find_unit(src, &unit, &rid, &dte, &edte,
 		    bootverbose);
 		if (error == 0) {
-			error = iommu_get_requester(src, &requester, &rid);
-			MPASS(error == 0);
-			ctx = amdiommu_get_ctx_for_dev(unit, src,
-			    rid, 0, false /* XXXKIB */, false, dte, edte);
+			ioctx = iommu_instantiate_ctx(AMD2IOMMU(unit), src, false);
+			if (ioctx != NULL)
+				ctx = IOCTX2CTX(ioctx);
 		}
 	}
 	if (ridp != NULL)