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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 12, 2023 at 03:48:08PM +0100, Will Deacon wrote: > I guess my wider point is that I'm not convinced that non-cacheable is > actually much better and I think we're going way off the deep end looking > at what particular implementations do and trying to justify to ourselves > that non-cacheable is safe, even though it's still a normal memory type > at the end of the day. When we went over this with ARM it became fairly clear there wasn't an official statement that Device-* is safe from uncontained failures. For instance, looking at the actual IP, our architects pointed out that ARM IP already provides ways for Device-* to trigger uncontained failures today. We then mutually concluded that KVM safe implementations must already be preventing uncontained failures for Device-* at the system level and that same prevention will carry over to NormalNC as well. IMHO, this seems to be a gap where ARM has not fully defined when uncontained failures are allowed and left that as an implementation choice. In other words, KVM safety around uncontained failure is not a property that can be reasoned about from the ARM architecture alone. > The current wording talks about use-cases (I get this) and error containment > (it's a property of the system) but doesn't talk at all about why Normal-NC > is the right result. Given that Device-* and NormalNC are equally implementation defined with regards to uncontained failures, NormalNC allows more VM functionality. Further, we have a broad agreement that this use case is important, and that NormalNC is the correct way to adress it. I think you are right to ask for more formality from ARM team but also we shouldn't hold up fixing real functional bugs in real shipping server ARM products. Jason _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel