From: "Andy Lutomirski" <luto@kernel.org>
To: "Thomas Gleixner" <tglx@linutronix.de>,
"Sohil Mehta" <sohil.mehta@intel.com>,
"the arch/x86 maintainers" <x86@kernel.org>
Cc: "Tony Luck" <tony.luck@intel.com>,
"Dave Hansen" <dave.hansen@intel.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>, "Jens Axboe" <axboe@kernel.dk>,
"Christian Brauner" <christian@brauner.io>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
"Shuah Khan" <shuah@kernel.org>, "Arnd Bergmann" <arnd@arndb.de>,
"Jonathan Corbet" <corbet@lwn.net>,
"Raj Ashok" <ashok.raj@intel.com>,
"Jacob Pan" <jacob.jun.pan@linux.intel.com>,
"Gayatri Kammela" <gayatri.kammela@intel.com>,
"Zeng Guang" <guang.zeng@intel.com>,
"Williams, Dan J" <dan.j.williams@intel.com>,
"Randy E Witt" <randy.e.witt@intel.com>,
"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
"Ramesh Thomas" <ramesh.thomas@intel.com>,
"Linux API" <linux-api@vger.kernel.org>,
linux-arch@vger.kernel.org,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
linux-kselftest@vger.kernel.org
Subject: Re: [RFC PATCH 11/13] x86/uintr: Introduce uintr_wait() syscall
Date: Fri, 01 Oct 2021 08:13:26 -0700 [thread overview]
Message-ID: <0364c572-4bc2-4538-8d65-485dbfa81f0d@www.fastmail.com> (raw)
In-Reply-To: <87pmsp5aqx.ffs@tglx>
On Fri, Oct 1, 2021, at 2:56 AM, Thomas Gleixner wrote:
> On Thu, Sep 30 2021 at 21:41, Andy Lutomirski wrote:
>> On Thu, Sep 30, 2021, at 5:01 PM, Thomas Gleixner wrote:
>
>> Now that I read the docs some more, I'm seriously concerned about this
>> XSAVE design. XSAVES with UINTR is destructive -- it clears UINV. If
>> we actually use this, then the whole last_cpu "preserve the state in
>> registers" optimization goes out the window. So does anything that
>> happens to assume that merely saving the state doesn't destroy it on
>> respectable modern CPUs XRSTORS will #GP if you XRSTORS twice, which
>> makes me nervous and would need a serious audit of our XRSTORS paths.
>
> I have no idea what you are fantasizing about. You can XRSTORS five
> times in a row as long as your XSTATE memory image is correct.
I'm just reading TFM, which is some kind of dystopian fantasy.
11.8.2.4 XRSTORS
Before restoring the user-interrupt state component, XRSTORS verifies that UINV is 0. If it is not, XRSTORS
causes a general-protection fault (#GP) before loading any part of the user-interrupt state component. (UINV
is IA32_UINTR_MISC[39:32]; XRSTORS does not check the contents of the remainder of that MSR.)
So if UINV is set in the memory image and you XRSTORS five times in a row, the first one will work assuming UINV was zero. The second one will #GP. And:
11.8.2.3 XSAVES
After saving the user-interrupt state component, XSAVES clears UINV. (UINV is IA32_UINTR_MISC[39:32];
XSAVES does not modify the remainder of that MSR.)
So if we're running a UPID-enabled user task and we switch to a kernel thread, we do XSAVES and UINV is cleared. Then we switch back to the same task and don't do XRSTORS (or otherwise write IA32_UINTR_MISC) and UINV is still clear.
And we had better clear UINV when running a kernel thread because the UPID might get freed or the kernel thread might do some CPL3 shenanigans (via EFI, perhaps? I don't know if any firmwares actually do this).
So all this seems to put UINV into the "independent" category of feature along with LBR. And the 512-byte wastes from extra copies of the legacy area and the loss of the XMODIFIED optimization will just be collateral damage.
next prev parent reply other threads:[~2021-10-01 15:13 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-13 20:01 [RFC PATCH 00/13] x86 User Interrupts support Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 01/13] x86/uintr/man-page: Include man pages draft for reference Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 02/13] Documentation/x86: Add documentation for User Interrupts Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 03/13] x86/cpu: Enumerate User Interrupts support Sohil Mehta
2021-09-23 22:24 ` Thomas Gleixner
2021-09-24 19:59 ` Sohil Mehta
2021-09-27 20:42 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 04/13] x86/fpu/xstate: Enumerate User Interrupts supervisor state Sohil Mehta
2021-09-23 22:34 ` Thomas Gleixner
2021-09-27 22:25 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 05/13] x86/irq: Reserve a user IPI notification vector Sohil Mehta
2021-09-23 23:07 ` Thomas Gleixner
2021-09-25 13:30 ` Thomas Gleixner
2021-09-26 12:39 ` Thomas Gleixner
2021-09-27 19:07 ` Sohil Mehta
2021-09-28 8:11 ` Thomas Gleixner
2021-09-27 19:26 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 06/13] x86/uintr: Introduce uintr receiver syscalls Sohil Mehta
2021-09-23 12:26 ` Greg KH
2021-09-24 0:05 ` Thomas Gleixner
2021-09-27 23:20 ` Sohil Mehta
2021-09-28 4:39 ` Greg KH
2021-09-28 16:47 ` Sohil Mehta
2021-09-23 23:52 ` Thomas Gleixner
2021-09-27 23:57 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 07/13] x86/process/64: Add uintr task context switch support Sohil Mehta
2021-09-24 0:41 ` Thomas Gleixner
2021-09-28 0:30 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 08/13] x86/process/64: Clean up uintr task fork and exit paths Sohil Mehta
2021-09-24 1:02 ` Thomas Gleixner
2021-09-28 1:23 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 09/13] x86/uintr: Introduce vector registration and uintr_fd syscall Sohil Mehta
2021-09-24 10:33 ` Thomas Gleixner
2021-09-28 20:40 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 10/13] x86/uintr: Introduce user IPI sender syscalls Sohil Mehta
2021-09-23 12:28 ` Greg KH
2021-09-28 18:01 ` Sohil Mehta
2021-09-29 7:04 ` Greg KH
2021-09-29 14:27 ` Sohil Mehta
2021-09-24 10:54 ` Thomas Gleixner
2021-09-13 20:01 ` [RFC PATCH 11/13] x86/uintr: Introduce uintr_wait() syscall Sohil Mehta
2021-09-24 11:04 ` Thomas Gleixner
2021-09-25 12:08 ` Thomas Gleixner
2021-09-28 23:13 ` Sohil Mehta
2021-09-28 23:08 ` Sohil Mehta
2021-09-26 14:41 ` Thomas Gleixner
2021-09-29 1:09 ` Sohil Mehta
2021-09-29 3:30 ` Andy Lutomirski
2021-09-29 4:56 ` Sohil Mehta
2021-09-30 18:08 ` Andy Lutomirski
2021-09-30 19:29 ` Thomas Gleixner
2021-09-30 22:01 ` Andy Lutomirski
2021-10-01 0:01 ` Thomas Gleixner
2021-10-01 4:41 ` Andy Lutomirski
2021-10-01 9:56 ` Thomas Gleixner
2021-10-01 15:13 ` Andy Lutomirski [this message]
2021-10-01 18:04 ` Sohil Mehta
2021-10-01 21:29 ` Thomas Gleixner
2021-10-01 23:00 ` Sohil Mehta
2021-10-01 23:04 ` Andy Lutomirski
2021-09-13 20:01 ` [RFC PATCH 12/13] x86/uintr: Wire up the user interrupt syscalls Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 13/13] selftests/x86: Add basic tests for User IPI Sohil Mehta
2021-09-13 20:27 ` [RFC PATCH 00/13] x86 User Interrupts support Dave Hansen
2021-09-14 19:03 ` Mehta, Sohil
2021-09-23 12:19 ` Greg KH
2021-09-23 14:09 ` Greg KH
2021-09-23 14:46 ` Dave Hansen
2021-09-23 15:07 ` Greg KH
2021-09-23 23:24 ` Sohil Mehta
2021-09-23 23:09 ` Sohil Mehta
2021-09-24 0:17 ` Sohil Mehta
2021-09-23 14:39 ` Jens Axboe
2021-09-29 4:31 ` Andy Lutomirski
2021-09-30 16:30 ` Stefan Hajnoczi
2021-09-30 17:24 ` Sohil Mehta
2021-09-30 17:26 ` Andy Lutomirski
2021-10-01 16:35 ` Stefan Hajnoczi
2021-10-01 16:41 ` Richard Henderson
2021-09-30 16:26 ` Stefan Hajnoczi
2021-10-01 0:40 ` Sohil Mehta
2021-10-01 8:19 ` Pavel Machek
2021-11-18 22:19 ` Sohil Mehta
2021-11-16 3:49 ` Prakash Sangappa
2021-11-18 21:44 ` Sohil Mehta
2021-12-22 16:17 ` Chrisma Pakha
2022-01-07 2:08 ` Sohil Mehta
2022-01-17 1:14 ` Chrisma Pakha
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=0364c572-4bc2-4538-8d65-485dbfa81f0d@www.fastmail.com \
--to=luto@kernel.org \
--cc=arnd@arndb.de \
--cc=ashok.raj@intel.com \
--cc=axboe@kernel.dk \
--cc=bp@alien8.de \
--cc=christian@brauner.io \
--cc=corbet@lwn.net \
--cc=dan.j.williams@intel.com \
--cc=dave.hansen@intel.com \
--cc=gayatri.kammela@intel.com \
--cc=guang.zeng@intel.com \
--cc=hpa@zytor.com \
--cc=jacob.jun.pan@linux.intel.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=ramesh.thomas@intel.com \
--cc=randy.e.witt@intel.com \
--cc=ravi.v.shankar@intel.com \
--cc=shuah@kernel.org \
--cc=sohil.mehta@intel.com \
--cc=tglx@linutronix.de \
--cc=tony.luck@intel.com \
--cc=x86@kernel.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).