From: Juergen Gross <jgross@suse.com>
To: "Li, Xin3" <xin3.li@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>
Cc: "tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"brgerst@gmail.com" <brgerst@gmail.com>,
"Bae, Chang Seok" <chang.seok.bae@intel.com>
Subject: Re: [PATCH v4 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index()
Date: Thu, 20 Oct 2022 06:53:27 +0200 [thread overview]
Message-ID: <7bbc19c8-3494-1770-d186-ce5a92d511aa@suse.com> (raw)
In-Reply-To: <BN6PR1101MB2161DD8F4F587C6FBFCA18EFA82B9@BN6PR1101MB2161.namprd11.prod.outlook.com>
[-- Attachment #1.1.1: Type: text/plain, Size: 1302 bytes --]
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
[-- Attachment #1.1.2: OpenPGP public key --]
[-- Type: application/pgp-keys, Size: 3149 bytes --]
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 495 bytes --]
next prev parent reply other threads:[~2022-10-20 4:53 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-19 9:50 [PATCH v4 0/5] Enable LKGS instruction Xin Li
2022-10-19 9:50 ` [PATCH v4 1/5] x86/cpufeature: add the cpu feature bit for LKGS Xin Li
2022-10-19 9:50 ` [PATCH v4 2/5] x86/opcode: add the LKGS instruction to x86-opcode-map Xin Li
2022-10-19 9:50 ` [PATCH v4 3/5] x86/gsseg: make asm_load_gs_index() take an u16 Xin Li
2022-10-19 9:50 ` [PATCH v4 4/5] x86/gsseg: move load_gs_index() to its own new header file Xin Li
2022-10-19 9:50 ` [PATCH v4 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index() Xin Li
2022-10-19 12:16 ` Juergen Gross
2022-10-19 17:45 ` Li, Xin3
2022-10-19 18:01 ` H. Peter Anvin
2022-10-20 4:54 ` Juergen Gross
2022-10-20 6:05 ` Li, Xin3
2022-10-20 4:53 ` Juergen Gross [this message]
2022-10-20 5:58 ` Li, Xin3
2022-10-20 6:08 ` Juergen Gross
2022-10-20 6:24 ` Li, Xin3
2022-10-19 10:23 [PATCH v4 0/5] x86: Enable LKGS instruction Xin Li
2022-10-19 10:23 ` [PATCH v4 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index() Xin Li
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=7bbc19c8-3494-1770-d186-ce5a92d511aa@suse.com \
--to=jgross@suse.com \
--cc=bp@alien8.de \
--cc=brgerst@gmail.com \
--cc=chang.seok.bae@intel.com \
--cc=dave.hansen@linux.intel.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
--cc=xin3.li@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).