* [PATCH v3 1/2] arm64: Add override for MMFR1.HAFDBS
2026-07-27 12:03 [PATCH v3 0/2] iommu/arm-smmu-v3: Fix SVA vs. HAFT issues Robin Murphy
@ 2026-07-27 12:03 ` Robin Murphy
2026-07-27 12:03 ` [PATCH v3 2/2] iommu/arm-smmu-v3: Add HAFT support for SVA Robin Murphy
1 sibling, 0 replies; 3+ messages in thread
From: Robin Murphy @ 2026-07-27 12:03 UTC (permalink / raw)
To: will, catalin.marinas, joro; +Cc: jpb, jgg, iommu, linux-arm-kernel
In general it might be nice to have the ability to disable hardware
access/dirty bit management for debugging or performance comparison
purposes without having to rebuild the kernel. However once FEAT_HAFT
comes into the picture we also start to have a real functional concern
where the decision to use HAFT based on the boot CPUs can prevent SVA
or late-onlining if SMMUs/CPUs are later found to lack HAFT support.
To that end, add the appropriate MMFR1 override, with an easy "nohaft"
alias for the significant case, partly since the feature/field naming
isn't the most obvious, but also so it could potentially be redirected
in future if someone wanted to attempt a higher-level means of turning
off just HAFT usage independently from FEAT_HDBSS.
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
v3: No change.
Documentation/admin-guide/kernel-parameters.txt | 3 +++
arch/arm64/kernel/pi/idreg-override.c | 2 ++
2 files changed, 5 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b5493a7f8f22..7f23e5b8dc44 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -565,6 +565,9 @@ Kernel parameters
arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack
support
+ arm64.nohaft [ARM64] Unconditionally disable Hardware managed Access
+ Flag for Table descriptors support
+
arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
Set instructions support
diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
index bc57b290e5e7..0e051fec5afe 100644
--- a/arch/arm64/kernel/pi/idreg-override.c
+++ b/arch/arm64/kernel/pi/idreg-override.c
@@ -64,6 +64,7 @@ static const struct ftr_set_desc mmfr1 __prel64_initconst = {
.override = &id_aa64mmfr1_override,
.fields = {
FIELD("vh", ID_AA64MMFR1_EL1_VH_SHIFT, mmfr1_vh_filter),
+ FIELD("hafdbs", ID_AA64MMFR1_EL1_HAFDBS_SHIFT, NULL),
{}
},
};
@@ -246,6 +247,7 @@ static const struct {
{ "arm64.nomte", "id_aa64pfr1.mte=0" },
{ "nokaslr", "arm64_sw.nokaslr=1" },
{ "rodata=off", "arm64_sw.rodataoff=1" },
+ { "arm64.nohaft", "id_aa64mmfr1.hafdbs=2" },
{ "arm64.nolva", "id_aa64mmfr2.varange=0" },
{ "arm64.no32bit_el0", "id_aa64pfr0.el0=1" },
{ "arm64.nompam", "id_aa64pfr0.mpam=0 id_aa64pfr1.mpam_frac=0" },
--
2.54.0.dirty
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH v3 2/2] iommu/arm-smmu-v3: Add HAFT support for SVA
2026-07-27 12:03 [PATCH v3 0/2] iommu/arm-smmu-v3: Fix SVA vs. HAFT issues Robin Murphy
2026-07-27 12:03 ` [PATCH v3 1/2] arm64: Add override for MMFR1.HAFDBS Robin Murphy
@ 2026-07-27 12:03 ` Robin Murphy
1 sibling, 0 replies; 3+ messages in thread
From: Robin Murphy @ 2026-07-27 12:03 UTC (permalink / raw)
To: will, catalin.marinas, joro; +Cc: jpb, jgg, iommu, linux-arm-kernel
Since table access flags cannot be software-managed, if process
pagetables are using HAFT then SVA must require the SMMU to support and
enable it too, otherwise page aging is liable to get out of whack.
For unbinding, we can't disable HAFT atomically with HA as might be
desired, but luckily we can get away with just not disabling HA either.
Cc: <stable@vger.kernel.org>
Fixes: 62df5870ebf7 ("arm64: Enable ARCH_HAS_NONLEAF_PMD_YOUNG")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
v3: Make all HTTU settings unconditional WRT mm.
.../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 24 +++++++++++--------
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 9 ++++++-
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 3 +++
3 files changed, 25 insertions(+), 11 deletions(-)
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
index 1ed8a6f29dc4..4cd60d3c450a 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
@@ -92,16 +92,6 @@ void arm_smmu_make_sva_cd(struct arm_smmu_cd *target,
target->data[1] = cpu_to_le64(virt_to_phys(mm->pgd) &
CTXDESC_CD_1_TTB0_MASK);
-
- /*
- * Enable Hardware Access and Dirty updates (DBM) if supported.
- * This is safe to enable by default, as PTE_WRITE and PTE_DBM
- * share the same bit.
- */
- if (master->smmu->features & ARM_SMMU_FEAT_HA)
- target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_HA);
- if (master->smmu->features & ARM_SMMU_FEAT_HD)
- target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_HD);
} else {
target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_EPD0);
@@ -114,6 +104,17 @@ void arm_smmu_make_sva_cd(struct arm_smmu_cd *target,
target->data[0] &=
cpu_to_le64(~(CTXDESC_CD_0_S | CTXDESC_CD_0_R));
}
+ /*
+ * Enable Hardware Access and Dirty updates (DBM) if supported. This is
+ * safe to enable by default, as PTE_WRITE and PTE_DBM share the same bit,
+ * while the EPD0 config can't get as far as fetching any PTEs anyway.
+ */
+ if (master->smmu->features & ARM_SMMU_FEAT_HA)
+ target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_HA);
+ if (master->smmu->features & ARM_SMMU_FEAT_HD)
+ target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_HD);
+ if (master->smmu->features & ARM_SMMU_FEAT_HAFT && system_supports_haft())
+ target->data[1] |= cpu_to_le64(CTXDESC_CD_1_HAFT);
/*
* MAIR value is pretty much constant and global, so we can just get it
@@ -211,6 +212,9 @@ bool arm_smmu_sva_supported(struct arm_smmu_device *smmu)
if (system_supports_bbml2_noabort())
feat_mask |= ARM_SMMU_FEAT_BBML2;
+ if (system_supports_haft())
+ feat_mask |= ARM_SMMU_FEAT_HAFT;
+
if ((smmu->features & feat_mask) != feat_mask)
return false;
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index a10affb483a4..14e5b3f08962 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -4921,10 +4921,14 @@ static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu)
static void arm_smmu_get_httu(struct arm_smmu_device *smmu, u32 reg)
{
- u32 fw_features = smmu->features & (ARM_SMMU_FEAT_HA | ARM_SMMU_FEAT_HD);
+ u32 fw_features = smmu->features & (ARM_SMMU_FEAT_HA | ARM_SMMU_FEAT_HD |
+ ARM_SMMU_FEAT_HAFT);
u32 hw_features = 0;
switch (FIELD_GET(IDR0_HTTU, reg)) {
+ case IDR0_HTTU_ACCESS_DIRTY_HAFT:
+ hw_features |= ARM_SMMU_FEAT_HAFT;
+ fallthrough;
case IDR0_HTTU_ACCESS_DIRTY:
hw_features |= ARM_SMMU_FEAT_HD;
fallthrough;
@@ -5256,6 +5260,9 @@ static int arm_smmu_device_acpi_probe(struct platform_device *pdev,
smmu->features |= ARM_SMMU_FEAT_COHERENCY;
switch (FIELD_GET(ACPI_IORT_SMMU_V3_HTTU_OVERRIDE, iort_smmu->flags)) {
+ case IDR0_HTTU_ACCESS_DIRTY_HAFT:
+ smmu->features |= ARM_SMMU_FEAT_HAFT;
+ fallthrough;
case IDR0_HTTU_ACCESS_DIRTY:
smmu->features |= ARM_SMMU_FEAT_HD;
fallthrough;
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index c909c9a88538..61a7df5afb99 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -40,6 +40,7 @@ struct arm_vsmmu;
#define IDR0_HTTU GENMASK(7, 6)
#define IDR0_HTTU_ACCESS 1
#define IDR0_HTTU_ACCESS_DIRTY 2
+#define IDR0_HTTU_ACCESS_DIRTY_HAFT 3
#define IDR0_COHACC (1 << 4)
#define IDR0_TTF GENMASK(3, 2)
#define IDR0_TTF_AARCH64 2
@@ -369,6 +370,7 @@ static inline unsigned int arm_smmu_cdtab_l2_idx(unsigned int ssid)
#define CTXDESC_CD_0_ASET (1UL << 47)
#define CTXDESC_CD_0_ASID GENMASK_ULL(63, 48)
+#define CTXDESC_CD_1_HAFT (1UL << 3)
#define CTXDESC_CD_1_TTB0_MASK GENMASK_ULL(51, 4)
/*
@@ -921,6 +923,7 @@ struct arm_smmu_device {
#define ARM_SMMU_FEAT_HD (1 << 22)
#define ARM_SMMU_FEAT_S2FWB (1 << 23)
#define ARM_SMMU_FEAT_BBML2 (1 << 24)
+#define ARM_SMMU_FEAT_HAFT (1 << 25)
u32 features;
#define ARM_SMMU_OPT_SKIP_PREFETCH (1 << 0)
--
2.54.0.dirty
^ permalink raw reply related [flat|nested] 3+ messages in thread