From: Dave Hansen <dave.hansen@intel.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Thomas Gleixner <tglx@linutronix.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
X86 ML <x86@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Rik van Riel <riel@redhat.com>,
Suresh Siddha <sbsiddha@gmail.com>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Fenghua Yu <fenghua.yu@intel.com>,
Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH 01/17] x86, fpu: wrap get_xsave_addr() to make it safer
Date: Tue, 24 Mar 2015 17:12:09 -0700 [thread overview]
Message-ID: <5511FD59.3040503@intel.com> (raw)
In-Reply-To: <CALCETrUxfd8brhWzBJSsSA=M1OHOSUWtu73gosPGZV9QgM6Z4Q@mail.gmail.com>
On 03/24/2015 04:52 PM, Andy Lutomirski wrote:
> On Tue, Mar 24, 2015 at 4:42 PM, Dave Hansen <dave.hansen@intel.com> wrote:
>> On 03/24/2015 03:28 PM, Andy Lutomirski wrote:
>>> Your function appears to be getting it for write (I assume that's what
>>> the unlazy_fpu is for), so I'd rather have it called
>>> tsk_get_xsave_field_for_write or something like that.
>>
>> It should be entirely read-only.
>>
>> For MPX (the only user of get_xsave_addr() iirc), we are only worried
>> about getting the status codes (and addresses) out of the bndstatus
>> register and making sure that the kernel-recorded bounds directory
>> address matches the bndcfgu (configuration) register.
>>
>> We don't ever write to the registers.
>
> So why are you unlazying it?
Oleg actually suggested it.
> IIUC, the xstae for current can be in one of three logical states:
>
> 1. Live in CPU regs. The in-memory copy is garbage and the state is
> in CPU regs.
> 2. Lazy. The in-memory copy and the CPU regs match. Writing to
> either copy is illegal.
> 3. In memory only. Writing to the in-memory copy is safe.
>
> IIUC, you want to read the xstate, do you're okay with #2 or #3. This
> would be tsk_get_xsave_field_for_read in my terminology.
>
> If you want to write the xstate, you'd need to be in state #3, which
> would be tsk_get_xsave_field_for_write.
>
> IIUC, unlazy_fpu just moves from from state 2 to 3.
I won't completely claim to understand what's going on with the FPU
code, but I think your analysis is a bit off.
unlazy_fpu() does __save_init_fpu() which (among other things) calls
xsave to dump the CPU registers to memory. That doesn't make any sense
to do if "The in-memory copy and the CPU regs match."
IOW, unlazy_fpu() is called when the in-memory copy is garbage and takes
us to a state where we can look at the in-memory copy.
next prev parent reply other threads:[~2015-03-25 0:12 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1427235664-25318-1-git-send-email-dave.hansen@intel.com>
[not found] ` <1427235664-25318-2-git-send-email-dave.hansen@intel.com>
2015-03-24 22:28 ` [PATCH 01/17] x86, fpu: wrap get_xsave_addr() to make it safer Andy Lutomirski
2015-03-24 23:42 ` Dave Hansen
2015-03-24 23:52 ` Andy Lutomirski
2015-03-25 0:12 ` Dave Hansen [this message]
2015-03-25 0:18 ` Andy Lutomirski
2015-03-25 0:20 ` Andy Lutomirski
2015-03-25 1:01 ` Rik van Riel
2015-03-25 9:08 ` Borislav Petkov
2015-03-25 14:15 ` Oleg Nesterov
2015-03-25 12:56 ` Oleg Nesterov
2015-03-25 12:45 ` Oleg Nesterov
2015-03-25 14:28 ` Dave Hansen
2015-03-25 17:11 ` Oleg Nesterov
2015-03-26 18:33 [PATCH 00/17] x86, mpx updates for 4.1 (take 2) Dave Hansen
2015-03-26 18:33 ` [PATCH 01/17] x86, fpu: wrap get_xsave_addr() to make it safer Dave Hansen
2015-03-27 15:15 ` Borislav Petkov
2015-03-27 16:35 ` Dave Hansen
2015-03-27 18:57 ` Oleg Nesterov
2015-03-27 21:52 [PATCH 00/17] x86, mpx updates for 4.1 (take 3) Dave Hansen
2015-03-27 21:52 ` [PATCH 01/17] x86, fpu: wrap get_xsave_addr() to make it safer Dave Hansen
2015-04-22 18:27 [PATCH 00/17] x86, mpx updates for 4.2 (take 5) Dave Hansen
2015-04-22 18:27 ` [PATCH 01/17] x86, fpu: wrap get_xsave_addr() to make it safer Dave Hansen
2015-04-25 9:31 ` Borislav Petkov
2015-05-05 17:27 ` Borislav Petkov
2015-05-08 17:42 ` Dave Hansen
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=5511FD59.3040503@intel.com \
--to=dave.hansen@intel.com \
--cc=dave.hansen@linux.intel.com \
--cc=fenghua.yu@intel.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=mingo@redhat.com \
--cc=oleg@redhat.com \
--cc=riel@redhat.com \
--cc=sbsiddha@gmail.com \
--cc=tglx@linutronix.de \
--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).