Re: [PATCH 0/3] target/ppc: fix tlb flushing race

[Nicholas Piggin]

On Thu Mar 28, 2024 at 3:31 PM AEST, Nicholas Piggin wrote:
> ppc broadcast tlb flushes should be synchronised with other vCPUs,
> like all other architectures that support such operations seem to
> be doing.
>
> Fixing ppc removes the last caller of the non-synced TLB flush
> variants, we can remove some dead code. I'd like to merge patch 1
> for 9.0, and hold patches 2 and 3 until 9.1 to avoid churn (unless
> someone prefers to remove the dead code asap).

Hmm, turns out to not be so simple, this in parts reverts
the fix in commit 4ddc104689b. Do other architectures
that use the _synced TLB flush variants have that same problem
with the TLB flush not actually flushing until the TB ends,
I wonder?

AFAIKS it seems like the right fix would be to use _synced, but
force a new TB at the end of the TLB flush instruction so the
flush will take effect on all CPUs before the next instruction?

In any case this is tricky enough and I only hit it with a
test program, so I'll leave it out of 9.0.

Thanks,
Nick