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Re: [Xen-devel] CONFIG_SCRUB_DEBUG=y + arm64 + livepatch = Xen BUG at page_alloc.c:738

On 09/12/2017 08:01 PM, Konrad Rzeszutek Wilk wrote:
On Mon, Sep 11, 2017 at 08:45:02PM -0400, Boris Ostrovsky wrote:

On 09/11/2017 07:55 PM, Konrad Rzeszutek Wilk wrote:

I've only been able to reproduce this on ARM64 (trying right now ARM32
as well), and not on x86.

If I compile Xen without CONFIG_SCRUB_DEBUG it works great. But if
enable it and try to load a livepatch it blows up in page_alloc.c:738

This is with origin/staging (d0291f3391)

Can you still reproduce this if you revert 307c3be?

Sadly yes - it still crashes. I didn't capture the serial output.

I honestly think the issue is that on ARM64 the "sleep" loop does not
wake up as often as on x86 (CC-ing Dariof who I believe observed this
with Credit2 and the wakeup.. something) - maybe he remembers the
details. Anyhow my theory is that the pages are not scrubbed at all
when they go in the idle loop as once it goes to sleep - it stays there.

There is no (well, should not be) any timing dependencies in how/whether pages are scrubbed. If a page doesn't get scrubbed because someone didn't wake up then it should be scrubbed in alloc_heap_pages(). So in this case the page is thought to be clean (_PGC_need_scrub is not set), but it is not.

Have you tried running a guest (or two), rebooting in a loop?

Another thing to try is to set need_scrub to true in free_heap_pages().


Ah, see commit 05c52278a7c92bc753d9fe32017e4961012b9f23

Maybe this is related?


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