linux-kernel - Re: [PATCH v10 00/18] Enable FSGSBASE instructions

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Date:   Mon, 11 May 2020 01:03:21 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Vegard Nossum <vegard.nossum@...cle.com>,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, luto@...nel.org,
        tony.luck@...el.com, chang.seok.bae@...el.com
Subject: Re: [PATCH v10 00/18] Enable FSGSBASE instructions

On Sun, May 10, 2020 at 05:50:28PM -0700, Andi Kleen wrote:
>> So this is a check that checks if you're running in user mode if
>> you have a debug trap with single step, but somehow it triggered
>> for a user segment.
>>
>> Probably the regs got corrupted.
>>
>> Sasha, I suspect you're missing a mov %rsp,%rdi somewhere in the
>> debug entry path that sets up the regs argument for the C code.
>
>... Ah never mind. Thomas has a better explanation.

FWIW, this series was heavily tested for the past few months to the
point that we're comfortable in enabling it for 3rd party users on
Azure:
https://bugs.launchpad.net/ubuntu/+source/linux-azure/+bug/1877425.

-- 
Thanks,
Sasha