linux-kernel - Re: Problems with Zen under Xen and recent Linux kernel improvements

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Date:   Sun, 5 Aug 2018 12:27:01 -0700
From:   Adam Novak <interfect@...il.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, boris.ostrovsky@...cle.com,
        x86@...nel.org
Subject: Re: Problems with Zen under Xen and recent Linux kernel improvements

Sorry, I am using Xen version 4.9.2, specifically 4.9.2-0ubuntu1.

I am seeing the bug with *kernel* version 4.15.0, and specifically
Ubuntu's tag Ubuntu-4.15.0-23.25. That appears to have the "x86/cpu:
Re-apply forced caps every time CPU caps are re-read" patch, but not
"x86/xen: Add call of speculative_store_bypass_ht_init() to PV paths".

I can try cherry-picking that commit. Are there other commits in
particular that might need to be pulled into the Ubuntu kernel to get
it to work?

On Tue, Jul 31, 2018 at 4:58 AM, Juergen Gross <jgross@...e.com> wrote:
> On 31/07/18 03:14, Adam Novak wrote:
>> Hello,
>>
>> I was advised to take this here, and to Boris Ostrovsky and Juergen
>> Gross, by Thomas Gleixner.
>>
>> I am having some trouble with the new speculation control code that
>> has been added to the Linux kernel, for AMD Zen CPUs. I am running an
>> AMD Ryzen 7 1700, and I am running Linux as a Xen dom0 (which is part
>> of the problem; the code seems to work fine running outside of Xen).
>>
>> I started having trouble on Ubuntu's commit
>> 3f6a3b035f91a22c0d3bd27630bf61eac9c8cf6c, "x86/speculation: Handle HT
>> correctly on AMD", which appears to be cherry-picked from
>> 1f50ddb4f4189243c05926b842dc1a0332195f31. Since that commit, my system
>> hangs during the boot process; it starts starting stuff up and trying
>> to mount things and printing "[OK]" messages, but then fairly early in
>> the boot process the kernel complains that it is "unable to handle
>> kernel NULL pointer deference at 000...0008"
>>
>> On my Ubuntu bug:
>>
>> https://bugs.launchpad.net/bugs/1777338
>>
>> I have a "Screenshot of the null pointer dereference message". It is
>> running into trouble during a spin lock in the new
>> speculative_store_bypass_update().
>>
>> Has anyone else seen this behavior on these CPUs under Xen (I am using 4.9)?
>
> You want at least 4.9.112, especially due to the missing patches
> "x86/xen: Add call of speculative_store_bypass_ht_init() to PV paths",
> "x86/cpu: Re-apply forced caps every time CPU caps are re-read"
>
> Juergen