From: Andrew Cooper <Andrew.Cooper3@citrix.com>
To: Ross Lagerwall <ross.lagerwall@citrix.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Jan Beulich <jbeulich@suse.com>,
Roger Pau Monne <roger.pau@citrix.com>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH] x86/cpu: Drop _init from *_cpu_cap functions
Date: Thu, 11 Aug 2022 10:34:55 +0000 [thread overview]
Message-ID: <e848e6a7-2c8e-d0d3-6aa8-24d9d78ae491@citrix.com> (raw)
In-Reply-To: <PH0PR03MB63827F5CFCCB8277405FD70BF0649@PH0PR03MB6382.namprd03.prod.outlook.com>
On 11/08/2022 11:30, Ross Lagerwall wrote:
>> From: Andrew Cooper <Andrew.Cooper3@citrix.com>
>> Sent: Thursday, August 11, 2022 11:21 AM
>> To: Ross Lagerwall <ross.lagerwall@citrix.com>; xen-devel@lists.xenproject.org <xen-devel@lists.xenproject.org>
>> Cc: Jan Beulich <jbeulich@suse.com>; Roger Pau Monne <roger.pau@citrix.com>; Wei Liu <wl@xen.org>
>> Subject: Re: [PATCH] x86/cpu: Drop _init from *_cpu_cap functions
>>
>> On 11/08/2022 11:17, Ross Lagerwall wrote:
>>> These functions may be called by init_amd() after the _init functions
>>> have been purged during CPU hotplug or PV shim boot so drop the _init.
>>>
>>> Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
>> Hmm. That's a bug in init_amd() I'd say. These really shouldn't be
>> used after __init.
>>
>> Which path exploded specifically?
> The stack trace was:
>
> setup_force_cpu_cap
> init_amd
> identify_cpu
> start_secondary
>
> In setup_force_cpu_cap() here:
>
> /*
> * On pre-CLFLUSHOPT AMD CPUs, CLFLUSH is weakly ordered with
> * everything, including reads and writes to address, and
> * LFENCE/SFENCE instructions.
> */
> if (!cpu_has_clflushopt)
> setup_force_cpu_cap(X86_BUG_CLFLUSH_MFENCE);
>
> which was recently introduced by:
>
> commit 062868a5a8b428b85db589fa9a6d6e43969ffeb9
> Author: Andrew Cooper <andrew.cooper3@citrix.com>
> Date: Thu Jun 9 14:23:07 2022 +0200
>
> x86/amd: Work around CLFLUSH ordering on older parts
Bah, and that was also backported in a security fix, to everything back
to 4.12 is broken.
> Should the fix rather be to guard that call with "if (c == &boot_cpu_data ..." ?
Yes please.
Sorry.
~Andrew
next prev parent reply other threads:[~2022-08-11 10:35 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-11 10:17 [PATCH] x86/cpu: Drop _init from *_cpu_cap functions Ross Lagerwall
2022-08-11 10:21 ` Andrew Cooper
2022-08-11 10:30 ` Ross Lagerwall
2022-08-11 10:34 ` Andrew Cooper [this message]
2022-08-11 10:59 ` Jan Beulich
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