lkml.org 
[lkml]   [2022]   [Oct]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v4 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index()
From
On 19.10.22 19:45, Li, Xin3 wrote:
>>> +static inline void __init lkgs_init(void) { #ifdef
>>> +CONFIG_PARAVIRT_XXL #ifdef CONFIG_X86_64
>>> + if (cpu_feature_enabled(X86_FEATURE_LKGS))
>>> + pv_ops.cpu.load_gs_index = native_lkgs;
>>
>> For this to work correctly when running as a Xen PV guest, you need to add
>>
>> setup_clear_cpu_cap(X86_FEATURE_LKGS);
>>
>> to xen_init_capabilities() in arch/x86/xen/enlighten_pv.c, as otherwise the Xen
>> specific .load_gs_index vector will be overwritten.
>
> Yeah, we definitely should add it to disable LKGS in a Xen PV guest.
>
> So does it mean that the Xen PV uses a black list during feature detection?
> If yes then new features are often required to be masked with an explicit
> call to setup_clear_cpu_cap.
>
> Wouldn't a white list be better?
> Then the job is more just on the Xen PV side, and it can selectively enable
> a new feature, sometimes with Xen PV specific handling code added.

This is not how it works. Feature detection is generic code, so we'd need to
tweak that for switching to a whitelist.

Additionally most features don't require any Xen PV specific handling. This is
needed for some paravirtualized privileged operations only. So switching to a
whitelist would add more effort.


Juergen

[unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2022-10-20 06:54    [W:0.070 / U:2.360 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site