On Wed, May 12, 2021 at 05:18:42PM +0100, Marc Zyngier wrote: > On 2021-05-12 17:03, Ricardo Koller wrote: > > On Wed, May 12, 2021 at 02:43:28PM +0100, Marc Zyngier wrote: > > > On 2021-05-12 13:59, Zenghui Yu wrote: > > > > Hi Eric, > > > > > > > > On 2021/5/6 20:30, Auger Eric wrote: > > > > > running the test on 5.12 I get > > > > > > > > > > ==== Test Assertion Failure ==== > > > > > aarch64/debug-exceptions.c:232: false > > > > > pid=6477 tid=6477 errno=4 - Interrupted system call > > > > > 1 0x000000000040147b: main at debug-exceptions.c:230 > > > > > 2 0x000003ff8aa60de3: ?? ??:0 > > > > > 3 0x0000000000401517: _start at :? > > > > > Failed guest assert: hw_bp_addr == PC(hw_bp) at > > > > > aarch64/debug-exceptions.c:105 > > > > > values: 0, 0x401794 > > > > > > > > FYI I can also reproduce it on my VHE box. And Drew's suggestion [*] > > > > seemed to work for me. Is the ISB a requirement of architecture? > > > > > > Very much so. Given that there is no context synchronisation (such as > > > ERET or an interrupt) in this code, the CPU is perfectly allowed to > > > delay the system register effect as long as it can. > > > > > > M. > > > -- > > > Jazz is not dead. It just smells funny... > > > > Thank you very much Eric, Zenghui, Marc, and Andrew (for the ISB > > suggestion)! > > > > As per Zenghui test, will send a V3 that includes the missing ISBs. > > Hopefully that will fix the issue for Eric as well. It's very > > interesting that the CPU seems to _always_ reorder those instructions. > > I suspect that because hitting the debug registers can be a costly > operation (it mobilises a lot of resources in the CPU), there is > a strong incentive to let it slide until there is an actual mandate > to commit the resource. > > It also means that SW can issue a bunch of these without too much > overhead, and only pay the cost *once*. > > Your N1 CPU seems to be less aggressive on this. Implement choice, > I'd say (it probably is more aggressive than TX2 on other things). > Also, QEMU will almost always hide these problems, due to the nature > of TCG. > > Thanks, > > M. > -- > Jazz is not dead. It just smells funny... Thank you, this is very informative.
