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arm64: Add override for ID_AA64MMFR4_EL1.NV_frac

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In a very unsurprising turn of events, there is a large class of
firmware that is totally unable to deal with FEAT_NV3, and doesn't
set the required SCR2_EL3.NV3En bit, leading to an UNDEF exception
or an unhandled trap to EL3, depending on the implementation.

Allow the unfortunate user to override ID_AA64MMFR4_EL1.NV_frac
and get a working system. Hopefully firmware will be fixed before
actually HW ships, but I have been there before... :-/

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://patch.msgid.link/20260730071022.296811-30-maz@kernel.org
Signed-off-by: Oliver Upton <oupton@kernel.org>
This commit is contained in:
Marc Zyngier 2026-07-30 08:10:22 +01:00 committed by Oliver Upton
parent 1f4a10ff90
commit 13c164acef
4 changed files with 15 additions and 1 deletions
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1
arch/arm64/include/asm/cpufeature.h
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@ -968,6 +968,7 @@ struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id);
extern struct arm64_ftr_override id_aa64mmfr0_override;
extern struct arm64_ftr_override id_aa64mmfr1_override;
extern struct arm64_ftr_override id_aa64mmfr2_override;
extern struct arm64_ftr_override id_aa64mmfr4_override;
extern struct arm64_ftr_override id_aa64pfr0_override;
extern struct arm64_ftr_override id_aa64pfr1_override;
extern struct arm64_ftr_override id_aa64zfr0_override;

4
arch/arm64/kernel/cpufeature.c
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@ -785,6 +785,7 @@ static const struct arm64_ftr_bits ftr_raz[] = {
struct arm64_ftr_override __read_mostly id_aa64mmfr0_override;
struct arm64_ftr_override __read_mostly id_aa64mmfr1_override;
struct arm64_ftr_override __read_mostly id_aa64mmfr2_override;
struct arm64_ftr_override __read_mostly id_aa64mmfr4_override;
struct arm64_ftr_override __read_mostly id_aa64pfr0_override;
struct arm64_ftr_override __read_mostly id_aa64pfr1_override;
struct arm64_ftr_override __read_mostly id_aa64zfr0_override;
@ -858,7 +859,8 @@ static const struct __ftr_reg_entry {
ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64MMFR2_EL1, ftr_id_aa64mmfr2,
&id_aa64mmfr2_override),
ARM64_FTR_REG(SYS_ID_AA64MMFR3_EL1, ftr_id_aa64mmfr3),
ARM64_FTR_REG(SYS_ID_AA64MMFR4_EL1, ftr_id_aa64mmfr4),
ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64MMFR4_EL1, ftr_id_aa64mmfr4,
&id_aa64mmfr4_override),
/* Op1 = 0, CRn = 10, CRm = 4 */
ARM64_FTR_REG(SYS_MPAMIDR_EL1, ftr_mpamidr),

1
arch/arm64/kernel/image-vars.h
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@ -51,6 +51,7 @@ PI_EXPORT_SYM(id_aa64isar2_override);
PI_EXPORT_SYM(id_aa64mmfr0_override);
PI_EXPORT_SYM(id_aa64mmfr1_override);
PI_EXPORT_SYM(id_aa64mmfr2_override);
PI_EXPORT_SYM(id_aa64mmfr4_override);
PI_EXPORT_SYM(id_aa64pfr0_override);
PI_EXPORT_SYM(id_aa64pfr1_override);
PI_EXPORT_SYM(id_aa64smfr0_override);

10
arch/arm64/kernel/pi/idreg-override.c
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@ -106,6 +106,15 @@ static const struct ftr_set_desc mmfr2 __prel64_initconst = {
},
};
static const struct ftr_set_desc mmfr4 __prel64_initconst = {
.name = "id_aa64mmfr4",
.override = &id_aa64mmfr4_override,
.fields = {
FIELD("nv_frac", ID_AA64MMFR4_EL1_NV_frac_SHIFT, NULL),
{}
},
};
static bool __init pfr0_sve_filter(u64 val)
{
/*
@ -220,6 +229,7 @@ PREL64(const struct ftr_set_desc, reg) regs[] __prel64_initconst = {
{ &mmfr0 },
{ &mmfr1 },
{ &mmfr2 },
{ &mmfr4 },
{ &pfr0 },
{ &pfr1 },
{ &isar1 },