Re: next/master bisection: baseline.login on rk3288-rock2-square
From: Ard Biesheuvel <ardb@kernel.org>
Date: 2021-02-04 14:29:03
Also in:
lkml
On Thu, 4 Feb 2021 at 15:09, Russell King - ARM Linux admin [off-list ref] wrote:
On Thu, Feb 04, 2021 at 12:26:44PM +0000, Marc Zyngier wrote:quoted
I agree. With set/way CMOs, there is no way to reach the PoC if it beyond the system cache, leading to an unbootable kernel. This is actually pretty well documented in the architecture, and it did bite us for the first time on XGene-1, 7 years ago.That may be, however we still do set/way maintenance to invalidate the L1 cache as that is required for ARMv7 to place the cache into a known state, as stated by the architecture reference manual.
Getting a certain cache at a certain level into a known state is a valid use of set/way ops, and is simply unnecessary when running under virtualization, but doesn't do any harm. Pushing contents of the cache hierarchy to main memory is *not* a valid use of set/way ops, and so there is no point in pretending that set/way ops will produce the same results as by-VA ops. Only the by-VA ops give the architectural guarantees that we rely on for correctness.
Arguably, that should be done by firmware, but when starting secondary CPUs, there are platforms out there which do not bring the L1 cache to a defined state. So we are pretty much stuck with doing set/way operations during CPU initialisation in the main kernel.
Indeed. And this is unfortunate, but not the end of the world.
If ARMv8 decides that this is not supportable, then that's a matter for ARMv8 to address without impacting the requirements of ARMv7.
I'm not sure what you mean here. The v7 architecture is crystal clear about the difference between set/way ops (managing a single cache), and by-VA ops (managing the 'cachedness' state of a memory region). The semantics are radically different, regardless of v7 vs v8 or AArch32 vs AArch64. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel