Re: [v3] powerpc/64s: ISAv3 initialize MMU registers before setting partition table

[Michael Ellerman <patch-notifications@ellerman.id.au>]

On Wed, 2017-12-06 at 08:21:14 UTC, Nicholas Piggin wrote:
> kexec can leave MMU registers set when booting into a new kernel, PIDR
> in particular. The boot sequence does not zero PIDR, so it only gets
> set when CPUs first switch to a userspace processes (until then it's
> running a kernel thread with effective PID = 0).
> 
> This leaves a window where a process table entry and page tables are
> set up due to user processes running on other CPUs, that happen to
> match with a stale PID. The CPU with that PID may cause speculative
> accesses that address quadrant 0, which will result in cached
> translations and PWC for that process, on a CPU which is not in the
> mm_cpumask and so they will not get invalidated properly.
> 
> The most common result is the kernel hanging in infinite page fault
> loops soon after kexec (usually in schedule_tail, which is usually the
> first non-speculative quardant 0 access to a new PID) due to a stale
> PWC. However being a stale translation error, it could result in
> anything up to security and data corruption problems.
> 
> Fix this by zeroing out PIDR at boot and kexec.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/371b80447ff33ddac392c189cf884a

cheers