From: Sean Christopherson <seanjc@google.com>
To: lkp@lists.01.org
Subject: Re: [x86/entry_32] aa93e2ad74: BUG:soft_lockup-CPU##stuck_for#s![systemd-logind:#]
Date: Wed, 12 Jan 2022 16:14:19 +0000 [thread overview]
Message-ID: <Yd7+W1gFbkBs5Lkd@google.com> (raw)
In-Reply-To: <Yd6ssarpDknV1r9z@hirez.programming.kicks-ass.net>
[-- Attachment #1: Type: text/plain, Size: 676 bytes --]
On Wed, Jan 12, 2022, Peter Zijlstra wrote:
> On Wed, Jan 12, 2022 at 01:28:58AM +0000, Sean Christopherson wrote:
> > The issue is that PARANOID_EXIT_TO_KERNEL_MODE in the handle_exception_return
> > path overwrites the entry stack data with the task stack data, restoring the "bad"
> > segment value.
>
> Oh gawd... that's terrible, and yes, that now makes perfect sense.
>
> However did you find that?
printf and running under QEMU, which has a interactive "monitor" that lets you
read/write guest memory and can also do VA=>PA translations. Code inspection
once I realized the value on the stack was being restored between the exception
fixup and the POP.
WARNING: multiple messages have this Message-ID (diff)
From: Sean Christopherson <seanjc@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: kernel test robot <oliver.sang@intel.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
x86@kernel.org, lkp@lists.01.org, lkp@intel.com
Subject: Re: [x86/entry_32] aa93e2ad74: BUG:soft_lockup-CPU##stuck_for#s![systemd-logind:#]
Date: Wed, 12 Jan 2022 16:14:19 +0000 [thread overview]
Message-ID: <Yd7+W1gFbkBs5Lkd@google.com> (raw)
In-Reply-To: <Yd6ssarpDknV1r9z@hirez.programming.kicks-ass.net>
On Wed, Jan 12, 2022, Peter Zijlstra wrote:
> On Wed, Jan 12, 2022 at 01:28:58AM +0000, Sean Christopherson wrote:
> > The issue is that PARANOID_EXIT_TO_KERNEL_MODE in the handle_exception_return
> > path overwrites the entry stack data with the task stack data, restoring the "bad"
> > segment value.
>
> Oh gawd... that's terrible, and yes, that now makes perfect sense.
>
> However did you find that?
printf and running under QEMU, which has a interactive "monitor" that lets you
read/write guest memory and can also do VA=>PA translations. Code inspection
once I realized the value on the stack was being restored between the exception
fixup and the POP.
next prev parent reply other threads:[~2022-01-12 16:14 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-06 8:35 [x86/entry_32] aa93e2ad74: BUG:soft_lockup-CPU##stuck_for#s![systemd-logind:#] kernel test robot
2022-01-06 8:35 ` kernel test robot
2022-01-11 11:11 ` Peter Zijlstra
2022-01-11 11:11 ` Peter Zijlstra
2022-01-12 1:28 ` Sean Christopherson
2022-01-12 1:28 ` Sean Christopherson
2022-01-12 10:25 ` Peter Zijlstra
2022-01-12 10:25 ` Peter Zijlstra
2022-01-12 16:14 ` Sean Christopherson [this message]
2022-01-12 16:14 ` Sean Christopherson
2022-01-12 10:55 ` [PATCH] x86/entry_32: Fix segment exceptions Peter Zijlstra
2022-01-12 10:55 ` Peter Zijlstra
2022-01-12 15:42 ` Borislav Petkov
2022-01-12 15:42 ` Borislav Petkov
2022-01-13 18:54 ` Andy Lutomirski
2022-01-13 18:54 ` Andy Lutomirski
2022-01-13 19:55 ` Peter Zijlstra
2022-01-13 19:55 ` Peter Zijlstra
2022-01-14 11:24 ` Borislav Petkov
2022-01-14 11:24 ` Borislav Petkov
2022-01-14 23:48 ` Andy Lutomirski
2022-01-14 23:48 ` Andy Lutomirski
2022-01-15 8:13 ` Borislav Petkov
2022-01-15 8:13 ` Borislav Petkov
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