[PATCH v3 1/2] arm64: Add override for MMFR1.HAFDBS
From: Robin Murphy <robin.murphy@arm.com>
Date: 2026-07-27 12:03:53
Also in:
linux-iommu
Subsystem:
arm64 port (aarch64 architecture), documentation, the rest · Maintainers:
Catalin Marinas, Will Deacon, Jonathan Corbet, Linus Torvalds
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