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arm64: Add override for MMFR1.HAFDBS

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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>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Robin Murphy 2026-07-27 13:03:28 +01:00 committed by Will Deacon
parent a86c36163c
commit 91038c83a2
2 changed files with 5 additions and 0 deletions
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3
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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

2
arch/arm64/kernel/pi/idreg-override.c
View File

@ -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" },