[seL4] Re: memory zero'ing

On Sat, Mar 11, 2023 at 10:56 AM Sam Leffler wrote:

On Fri, Mar 10, 2023 at 3:28 PM Kent Mcleod wrote:

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On Sat, 11 Mar 2023, 09:40 Sam Leffler via Devel, wrote:

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I'm chasing an issue that looks like retype'd memory has nonsense data. If I read the kernel code correctly it looks like the object returned by an seL4_UntypeRetype syscall should be zero'd (looks to happen when an untyped memory object is reset here https://github.com/seL4/seL4/blob/master/src/object/untyped.c#L254). Is that correct? I don't see anything called out in the manual

If the untyped isn't device untyped then it should be zeroed before it is typed into an object. Device untyped is not allowed to be accessed by the kernel and so is not written to.

When are you observing the odd behaviour?

I've got a stress test that forces lots of memory recycling by creating, running & tearing down applications. I repeatedly see a particular point in the test (after memory starts being recycled) where an app gets an instruction fault. Narrowing the issue has been challenging so I'm questioning everything (including cache handling). This is all anonymous memory.

Is the instruction fault triggered deterministically when the system is stressed? What sort of instruction fault, prefetch data fault or undefined instruction? Because it's happening with teardown and recreate of applications, it could be more likely caused by bad page table cache maintenance rather than clean on the UT retype. Kent.

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-Sam _______________________________________________ Devel mailing list -- devel@sel4.systems To unsubscribe send an email to devel-leave@sel4.systems