From: "Bae, Chang Seok" <chang.seok.bae@intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Juergen Gross <jgross@suse.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <ak@linux.intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Metzger, Markus T" <markus.t.metzger@intel.com>,
"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [v3 04/12] x86/fsgsbase/64: Enable FSGSBASE instructions in the helper functions
Date: Thu, 25 Oct 2018 23:03:31 +0000 [thread overview]
Message-ID: <6CD573FD-3B38-45B1-9DC6-B5F0E9087FB4@intel.com> (raw)
In-Reply-To: <CALCETrVdxKsSgU8zeyn7DO-1toO770yZbEAPTGOtF0FvPfQOXg@mail.gmail.com>
> On Oct 25, 2018, at 16:00, Andy Lutomirski <luto@kernel.org> wrote:
>
> On Thu, Oct 25, 2018 at 12:32 AM Bae, Chang Seok
> <chang.seok.bae@intel.com> wrote:
>>
>>
>>> On Oct 24, 2018, at 12:16, Andy Lutomirski <luto@kernel.org> wrote:
>>>
>>> On Tue, Oct 23, 2018 at 11:43 AM Chang S. Bae <chang.seok.bae@intel.com> wrote:
>>>> void x86_fsbase_write_cpu(unsigned long fsbase)
>>>> {
>>>> - /*
>>>> - * Set the selector to 0 as a notion, that the segment base is
>>>> - * overwritten, which will be checked for skipping the segment load
>>>> - * during context switch.
>>>> - */
>>>> - loadseg(FS, 0);
>>>> - wrmsrl(MSR_FS_BASE, fsbase);
>>>> + if (static_cpu_has(X86_FEATURE_FSGSBASE)) {
>>>> + wrfsbase(fsbase);
>>>> + } else {
>>>> + /*
>>>> + * Set the selector to 0 as a notion, that the segment base is
>>>> + * overwritten, which will be checked for skipping the segment load
>>>> + * during context switch.
>>>> + */
>>>> + loadseg(FS, 0);
>>>> + wrmsrl(MSR_FS_BASE, fsbase);
>>>> + }
>>>> }
>>>>
>>>> void x86_gsbase_write_cpu_inactive(unsigned long gsbase)
>>>> {
>>>> - /* Set the selector to 0 for the same reason as %fs above. */
>>>> - loadseg(GS, 0);
>>>> - wrmsrl(MSR_KERNEL_GS_BASE, gsbase);
>>>> + if (static_cpu_has(X86_FEATURE_FSGSBASE)) {
>>>> + wr_inactive_gsbase(gsbase);
>>>> + } else {
>>>> + /* Set the selector to 0 for the same reason as %fs above. */
>>>> + loadseg(GS, 0);
>>>> + wrmsrl(MSR_KERNEL_GS_BASE, gsbase);
>>>
>>> I still don't get what this code is trying to do. See other email. I
>>> think it will straight up crash the kernel on some CPUs, since writing
>>> 0 to %%gs will zero out the *active* base on some CPUs.
>>>
>>
>> On those CPUs, how the old do_arch_prctl_64() worked?
>> loadseg(GS, 0) eventually hits the native_load_gs_index entry, where actual
>> mov …, %gs is wrapped by two SWAPGSes. So, it won’t cause the side effect
>> of overwriting the *active* base, I think.
>>
>>> I think that, if you really want some fancy optimization for the
>>> non-FSGSBASE case, you need to pull that out into the callers of these
>>> helpers.
>>
>
> I was thinking of loadsegment, not loadseg. Sorry!
No problem! Appreciate your reviews.
Chang
next prev parent reply other threads:[~2018-10-25 23:03 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-23 18:42 [v3 00/12] x86: Enable FSGSBASE instructions Chang S. Bae
2018-10-23 18:42 ` [v3 01/12] taint: Introduce a new taint flag (insecure) Chang S. Bae
2018-10-24 18:50 ` Andy Lutomirski
2018-10-23 18:42 ` [v3 02/12] x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Chang S. Bae
2018-10-24 18:51 ` Andy Lutomirski
2018-10-23 18:42 ` [v3 03/12] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions Chang S. Bae
2018-10-24 18:53 ` Andy Lutomirski
2018-10-24 19:21 ` Andi Kleen
2018-10-25 23:14 ` Andy Lutomirski
2018-10-25 23:31 ` Linus Torvalds
2018-10-26 0:09 ` Andy Lutomirski
2018-10-23 18:42 ` [v3 04/12] x86/fsgsbase/64: Enable FSGSBASE instructions in the helper functions Chang S. Bae
2018-10-24 19:16 ` Andy Lutomirski
2018-10-24 19:41 ` [Xen-devel] " Andrew Cooper
2018-10-25 6:09 ` Juergen Gross
2018-10-25 23:08 ` Andrew Cooper
2018-10-25 23:11 ` Andy Lutomirski
2018-10-25 23:14 ` Andrew Cooper
2018-10-25 7:32 ` Bae, Chang Seok
2018-10-25 23:00 ` Andy Lutomirski
2018-10-25 23:03 ` Bae, Chang Seok [this message]
2018-10-25 23:16 ` Andy Lutomirski
2018-10-23 18:42 ` [v3 05/12] x86/fsgsbase/64: Preserve FS/GS state in __switch_to() if FSGSBASE is on Chang S. Bae
2018-10-24 19:21 ` Andy Lutomirski
2018-10-24 19:36 ` Bae, Chang Seok
2018-10-23 18:42 ` [v3 06/12] x86/fsgsbase/64: When copying a thread, use the FSGSBASE instructions if available Chang S. Bae
2018-10-23 18:42 ` [v3 07/12] x86/fsgsbase/64: Introduce the new FIND_PERCPU_BASE macro Chang S. Bae
2018-10-26 0:25 ` Andy Lutomirski
2018-10-26 0:59 ` Nadav Amit
2018-10-23 18:42 ` [v3 08/12] x86/fsgsbase/64: Use the per-CPU base as GSBASE at the paranoid_entry Chang S. Bae
2018-10-23 18:42 ` [v3 09/12] selftests/x86/fsgsbase: Test WRGSBASE Chang S. Bae
2018-10-23 18:42 ` [v3 10/12] x86/fsgsbase/64: Enable FSGSBASE by default and add a chicken bit Chang S. Bae
2018-10-23 18:42 ` [v3 11/12] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Chang S. Bae
2018-10-23 18:42 ` [v3 12/12] x86/fsgsbase/64: Add documentation for FSGSBASE Chang S. Bae
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=6CD573FD-3B38-45B1-9DC6-B5F0E9087FB4@intel.com \
--to=chang.seok.bae@intel.com \
--cc=ak@linux.intel.com \
--cc=boris.ostrovsky@oracle.com \
--cc=dave.hansen@linux.intel.com \
--cc=hpa@zytor.com \
--cc=jgross@suse.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=markus.t.metzger@intel.com \
--cc=mingo@kernel.org \
--cc=ravi.v.shankar@intel.com \
--cc=tglx@linutronix.de \
--cc=xen-devel@lists.xenproject.org \
/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).