Re: [PATCH 0/3] ARM: v7: get rid of boot time mini stack
From: Nicolas Pitre <nico@fluxnic.net>
Date: 2021-02-08 23:12:31
On Mon, 8 Feb 2021, Ard Biesheuvel wrote:
The v7 boot code uses a small chunk of BSS to preserve some register contents across a call to v7_invalidate_l1 that occurs with the MMU and caches disabled. Memory accesses in such cases are tricky on v7+, given that the architecture permits some unintuitive behaviors (it is implementation defined whether accesses done with the MMU and caches off may hit in the caches, and on SoCs that incorporate off-core system caches, this behavior appears to be different even between cache levels). Also, cache invalidation is not safe under virtualization if the intent is to retain stores issued directly to DRAM, given that the hypervisor may upgrade invalidate operations to clean+invalidate, resulting in DRAM contents to be overwritte by the dirty cachelines that we were trying to evict in the first place. So let's address this issue, by removing the need for this stack to exist in the first place: v7_invalidate_l1 can be rewritten to use fewer registers, which means fewer registers need to be preserved, and we have enough spare registers available.
That is excellent. I wonder why r1-r3 were preserved though. Nicolas _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel