[PATCH] arm64: cpufeature: Fix missing ZFR0 in __read_sysreg_by_encoding()

[PATCH] arm64: cpufeature: Fix missing ZFR0 in __read_sysreg_by_encoding()

[Dave Martin]

In commit 06a916feca2b ("arm64: Expose SVE2 features for
userspace"), new hwcaps are added that are detected via fields in
the SVE-specific ID register ID_AA64ZFR0_EL1.

In order to check compatibility of secondary cpus with the hwcaps
established at boot, the cpufeatures code uses
__read_sysreg_by_encoding() to read this ID register based on the
sys_reg field of the arm64_elf_hwcaps[] table.

This leads to a kernel splat if an hwcap uses an ID register that
__read_sysreg_by_encoding() doesn't explicitly handle, as now
happens when exercising cpu hotplug on an SVE2-capable platform.

So fix it by adding the required case in there.

Fixes: 06a916feca2b ("arm64: Expose SVE2 features for userspace")
Signed-off-by: Dave Martin <Dave.Martin@arm.com>

---

There is a broader question about how to avoid this happening again, but
I couldn't see an obvious solution so far.
---
 arch/arm64/kernel/cpufeature.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index ca27e08..80babf4 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -830,6 +830,7 @@ static u64 __read_sysreg_by_encoding(u32 sys_id)
 
 	read_sysreg_case(SYS_ID_AA64PFR0_EL1);
 	read_sysreg_case(SYS_ID_AA64PFR1_EL1);
+	read_sysreg_case(SYS_ID_AA64ZFR0_EL1);
 	read_sysreg_case(SYS_ID_AA64DFR0_EL1);
 	read_sysreg_case(SYS_ID_AA64DFR1_EL1);
 	read_sysreg_case(SYS_ID_AA64MMFR0_EL1);
-- 
2.1.4


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