[PATCHv3 5/5] arm64: add runtime system sanity checks
Christopher Covington
cov at codeaurora.org
Thu Jun 26 13:29:10 PDT 2014
Hi Mark,
On 06/26/2014 11:18 AM, Mark Rutland wrote:
> Unexpected variation in certain system register values across CPUs is an
> indicator of potential problems with a system. The kernel expects CPUs
> to be mostly identical in terms of supported features, even in systems
> with heterogeneous CPUs, with uniform instruction set support being
> critical for the correct operation of userspace.
>
> To help detect issues early where hardware violates the expectations of
> the kernel, this patch adds simple runtime sanity checks on important ID
> registers in the bring up path of each CPU.
>
> Where CPUs are fundamentally mismatched, set TAINT_CPU_OUT_OF_SPEC.
> Given that the kernel assumes CPUs are identical feature wise, let's not
> pretend that we expect such configurations to work. Supporting such
> configurations would require massive rework, and hopefully they will
> never exist.
>
> Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> ---
> arch/arm64/kernel/cpuinfo.c | 92 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 92 insertions(+)
>
> diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> + /* If different, timekeeping will be broken (especially with KVM) */
> + diff |= CHECK(cntfrq, boot, cur, cpu);
You're calling this a "CPU feature" but I thought this was purely a firmware
setting. Does the architecture even allow hardware to program this register?
Additionally, in arch_timer_detect_rate it appears that a device tree setting
takes precedence, but you're not checking that.
> + /*
> + * Mismatched CPU features are a recipe for disaster. Don't even
> + * pretend to support them.
> + */
> + WARN_TAINT_ONCE(diff, TAINT_CPU_OUT_OF_SPEC,
> + "Unsupported CPU feature variation.");
> +}
Christopher
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