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Re: [PATCH] x86/cpu: Drop _init from *_cpu_cap functions
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- Date: Thu, 11 Aug 2022 10:30:51 +0000
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
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- Thread-topic: [PATCH] x86/cpu: Drop _init from *_cpu_cap functions
> From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
> Sent: Thursday, August 11, 2022 11:21 AM
> To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>;
> xen-devel@xxxxxxxxxxxxxxxxxxxx <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>; Roger Pau Monne <roger.pau@xxxxxxxxxx>;
> Wei Liu <wl@xxxxxxx>
> 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@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
Date: Thu Jun 9 14:23:07 2022 +0200
x86/amd: Work around CLFLUSH ordering on older parts
Should the fix rather be to guard that call with "if (c == &boot_cpu_data ..." ?
Ross
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