* Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> This demotes an OOPS and likely panic due to a failed non-"safe" MSR
> access to a WARN_ON_ONCE and a return of poisoned values (in the
> RDMSR case). We still write a pr_info entry unconditionally for
> debugging.
>
> To be clear, this type of failure should *not* happen. This patch
> exists to minimize the chance of nasty undebuggable failures due on
> systems that used to work due to a now-fixed CONFIG_PARAVIRT=y bug.
> + if (opcode == 0x320f) {
> + /* RDMSR */
> + pr_info("bad kernel RDMSR from non-existent MSR 0x%x",
> + (unsigned int)regs->cx);
> + if (!panic_on_oops) {
> + WARN_ON_ONCE(true);
> +
> + /* Patch it up with deterministic poison. */
> + regs->ax = 0x5aadc0de;
> + regs->dx = 0x8badf00d;
> + regs->ip += 2;
> + return true;
IMHO this should really not poison the result, but use zero as the result.
The poison might randomly indicate 'present' feature in various registers that
might be accessed in a buggy way. Don't send the code further down into la-la-land
by giving it a 'success'.
And yes, zero can mean success too, but we have to pick a side here ...
The warning will be enough to fix these ups, people (and in particular distro
testing people) will be watching out for them.
Thanks,
Ingo
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