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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/riscv/uabi.rst | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/Documentation/riscv/uabi.rst b/Documentation/riscv/uabi.rst index 8960fac42c40..54d199dce78b 100644 --- a/Documentation/riscv/uabi.rst +++ b/Documentation/riscv/uabi.rst @@ -42,6 +42,26 @@ An example string following the order is:: rv64imadc_zifoo_zigoo_zafoo_sbar_scar_zxmbaz_xqux_xrux +"isa" and "hart isa" lines in /proc/cpuinfo +------------------------------------------- + +The "isa" line in /proc/cpuinfo describes the lowest common denominator of +RISC-V ISA extensions recognized by the kernel and implemented on all harts. The +"hart isa" line, in contrast, describes the set of extensions recognized by the +kernel on the particular hart being described, even if those extensions may not +be present on all harts in the system. + +In both lines, the presence of an extension guarantees only that the hardware +has the described capability. Additional kernel support or policy changes may be +required before an extension's capability is fully usable by userspace programs. +Similarly, for S-mode extensions, presence in one of these lines does not +guarantee that the kernel is taking advantage of the extension, or that the +feature will be visible in guest VMs managed by this kernel. + +Inversely, the absence of an extension in these lines does not necessarily mean +the hardware does not support that feature. The running kernel may not recognize +the extension, or may have deliberately removed it from the listing. + Misaligned accesses ------------------- |