From: "Bae, Chang Seok" <chang.seok.bae@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: "Lutomirski, Andy" <luto@kernel.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@kernel.org" <mingo@kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"Brown, Len" <len.brown@intel.com>,
"Hansen, Dave" <dave.hansen@intel.com>,
"Macieira, Thiago" <thiago.macieira@intel.com>,
"Liu, Jing2" <jing2.liu@intel.com>,
"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v9 08/26] x86/fpu/xstate: Introduce helpers to manage the XSTATE buffer dynamically
Date: Fri, 13 Aug 2021 08:04:54 +0000 [thread overview]
Message-ID: <2BF12EDA-89F0-40F7-B63E-50ADD0262164@intel.com> (raw)
In-Reply-To: <YRV6M1I/GMXwuJqW@zn.tnic>
On Aug 12, 2021, at 12:44, Borislav Petkov <bp@alien8.de> wrote:
> On Fri, Jul 30, 2021 at 07:59:39AM -0700, Chang S. Bae wrote:
>>
>> --- a/arch/x86/include/asm/trace/fpu.h
>> +++ b/arch/x86/include/asm/trace/fpu.h
>> @@ -89,6 +89,11 @@ DEFINE_EVENT(x86_fpu, x86_fpu_xstate_check_failed,
>> TP_ARGS(fpu)
>> );
>>
>> +DEFINE_EVENT(x86_fpu, x86_fpu_xstate_alloc_failed,
>> + TP_PROTO(struct fpu *fpu),
>> + TP_ARGS(fpu)
>
> Last time I said:
>
> "Yes, add it when it is really needed. Not slapping it proactively and
> hoping for any potential usage."
>
> Why is that thing still here?!
There was no clear path to emit the error code before. I thought that’s the
reason for this tracepoint. But now a signal or an error code return is
established. I should have removed it along with the change.
>> + * @mask: This bitmap tells which components reserved in the buffer.
>
> are reserved?
>
> What's this notion of reservation here? The mask is dictating what gets
> reserved in the buffer or what?
>
> Looking at the usage, that mask is simply saying which components are
> going to be saved in the buffer. So all this "reserved" bla is only
> confusing - drop it.
Okay. I remember this “reserved” started from a changelog. With your
confusion, let me also make sure all is removed.
>> + *
>> + * Available once those arrays for the offset, size, and alignment info are
>> + * set up, by setup_xstate_features().
>> + *
>> + * Returns: The buffer size
>> + */
>> +unsigned int get_xstate_size(u64 mask)
>> +{
>> + unsigned int size;
>> + int i, nr;
>> +
>> + if (!mask)
>> + return 0;
>> +
>> + /*
>> + * The minimum buffer size excludes the dynamic user state. When a
>> + * task uses the state, the buffer can grow up to the max size.
>> + */
>> + if (mask == (xfeatures_mask_all & ~xfeatures_mask_user_dynamic))
>> + return get_xstate_config(XSTATE_MIN_SIZE);
>> + else if (mask == xfeatures_mask_all)
>> + return get_xstate_config(XSTATE_MAX_SIZE);
>> +
>> + nr = fls64(mask) - 1;
>> +
>> + if (!boot_cpu_has(X86_FEATURE_XSAVES))
>
> cpu_feature_enabled()
>
>> + return xstate_offsets[nr] + xstate_sizes[nr];
>
> From all the superfluous commenting, where a comment is really needed is
> here but there's none.
>
> What's that doing? No compacted states enabled so take the offset and
> size of the *last* state and use that as the buffer size?
Yes, each state offset in the non-compacted format is fixed in a machine
regardless of RFBM. So, simply take the size like that.
>> +
>> + if ((xfeatures_mask_all & (BIT_ULL(nr + 1) - 1)) == mask)
> ^^^^^^^^^^^^^^^^^^^^^
>
> That thing looks like a GENMASK_ULL() thing. Use it?
Looks like I was not familiar with this macro:
if ((xfeatures_mask_all & GENMASK_ULL(nr, 0)) == mask)
> Also, what is that test doing?!
>
> If a mask up to nr ANDed with mask_all is == mask?!
>
> You need to explain yourself a lot more here what you're doing. Why
> those two special cases if you can simply iterate over the extended
> states and be done with it? Except maybe the first two special cases
> which are trivial...
xstate_comp_offset[] comes from the compacted format with xfeatures_mask_all.
If feature bits are all the same up to ‘nr', this recorded offset can be taken.
But it might be better to simplify this hunk for readability. I suspect its
call sites are not that performance-critical.
>> @@ -848,6 +908,9 @@ void __init fpu__init_system_xstate(void)
>> if (err)
>> goto out_disable;
>>
>> + /* Make sure init_task does not include the dynamic user states. */
>
> My constant review question: why?
Every task’s state_mask should begin as aligned with the default buffer.
fpu_clone() sets this for all, except init_task.
Maybe:
“Make sure init_task’s state_mask aligned with its __default_state"
>> + current->thread.fpu.state_mask = (xfeatures_mask_all & ~xfeatures_mask_user_dynamic);
>> +
>> +/**
>> + * alloc_xstate_buffer - Allocate a buffer with the size calculated from
>
> This name doesn't even begin to tell me that this function deals with
> enlarging the xstate buffer with dynamic states. How is the caller
> supposed to know?
How about enlarge_xstate_buffer() or realloc_xstate_buffer()?
>
> Also, you need to move all possible xfeatures_mask_user_dynamic querying
> inside it so that its user doesn't have to do it. I'm looking at the
> callsite in xstateregs_set().
The query is intended to check whether the xstate buffer is fully expanded or
not -- no need to enlarge.
If the buffer is already the maximum, the code to retrieve XSTATE_BV, this
call, etc should be skipped there.
If the query is moved here, I guess this call site code becomes a bit ugly.
> The other callsite in exc_device_not_available() seems to not check the
> dynamic states but uses only XFD. I guess I'll parse that properly when
> I get there but right now I have no clue why you're not checking the
> dynamic mask there.
In this case, I think it makes sense to move it in this function. But not
clear how well adjust the above case yet.
>> +int alloc_xstate_buffer(struct fpu *fpu, u64 mask)
>> +{
>> + union fpregs_state *state;
>> + unsigned int oldsz, newsz;
>> + u64 state_mask;
>> +
>> + state_mask = fpu->state_mask | mask;
>> +
>> + oldsz = get_xstate_size(fpu->state_mask);
>> + newsz = get_xstate_size(state_mask);
>> +
>> + if (oldsz >= newsz)
>> + return 0;
>
> Why?
>
> Why not simply:
>
> if (fpu->state_mask == mask)
> return 0;
>
> /* vzalloc */
>
> /* free the old buffer */
> free_xstate_buffer(fpu);
>
> fpu->state = state;
> ...
>
> ?
>
> Our FPU code is a mess - you should try not to make it an even bigger
> one without a good reason.
Okay, maybe get_xstate_size() is overkill. But I think a sanity-check like
this:
if ((mask & fpu->state_mask) == mask)
return 0;
>> +
>> + state = vzalloc(newsz);
>> + if (!state) {
>> + /*
>> + * When allocation requested from #NM, the error code may
>> + * not be populated well. Then, this tracepoint is useful
>> + * for providing the failure context.
>> + */
>> + trace_x86_fpu_xstate_alloc_failed(fpu);
>> + return -ENOMEM;
>
> What happens with the old buffer here? It seems we leak it…
No, it is still pointed by fpu->state and will be freed in the exit path.
Thanks,
Chang
next prev parent reply other threads:[~2021-08-13 8:06 UTC|newest]
Thread overview: 91+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-30 14:59 [PATCH v9 00/26] x86: Support Intel Advanced Matrix Extensions Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 01/26] x86/fpu/xstate: Modify the initialization helper to handle both static and dynamic buffers Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 02/26] x86/fpu/xstate: Modify state copy helpers " Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 03/26] x86/fpu/xstate: Modify address finders " Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 04/26] x86/fpu/xstate: Add a new variable to indicate dynamic user states Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 05/26] x86/fpu/xstate: Add new variables to indicate dynamic XSTATE buffer size Chang S. Bae
2021-08-12 15:03 ` Borislav Petkov
2021-07-30 14:59 ` [PATCH v9 06/26] x86/fpu/xstate: Calculate and remember dynamic XSTATE buffer sizes Chang S. Bae
2021-08-12 16:36 ` Borislav Petkov
2021-07-30 14:59 ` [PATCH v9 07/26] x86/fpu/xstate: Convert the struct fpu 'state' field to a pointer Chang S. Bae
2021-08-12 17:09 ` Borislav Petkov
2021-07-30 14:59 ` [PATCH v9 08/26] x86/fpu/xstate: Introduce helpers to manage the XSTATE buffer dynamically Chang S. Bae
2021-08-12 19:44 ` Borislav Petkov
2021-08-13 8:04 ` Bae, Chang Seok [this message]
2021-08-13 10:04 ` Borislav Petkov
2021-08-13 19:43 ` Bae, Chang Seok
2021-08-18 9:28 ` Borislav Petkov
2021-08-18 19:46 ` Bae, Chang Seok
2021-08-25 16:01 ` Bae, Chang Seok
2021-08-30 17:07 ` Borislav Petkov
2021-08-30 23:39 ` Bae, Chang Seok
2021-08-16 18:33 ` Bae, Chang Seok
2021-08-16 18:53 ` Borislav Petkov
2021-08-30 17:45 ` Dave Hansen
2021-08-30 23:39 ` Bae, Chang Seok
2021-07-30 14:59 ` [PATCH v9 09/26] x86/fpu/xstate: Update the XSTATE save function to support dynamic states Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 10/26] x86/fpu/xstate: Update the XSTATE buffer address finder " Chang S. Bae
2021-08-18 11:33 ` Borislav Petkov
2021-08-18 19:47 ` Bae, Chang Seok
2021-08-30 17:18 ` Borislav Petkov
2021-08-30 23:38 ` Bae, Chang Seok
2021-07-30 14:59 ` [PATCH v9 11/26] x86/fpu/xstate: Update the XSTATE context copy function " Chang S. Bae
2021-08-18 12:03 ` Borislav Petkov
2021-08-18 19:47 ` Bae, Chang Seok
2021-07-30 14:59 ` [PATCH v9 12/26] x86/fpu/xstate: Use feature disable (XFD) to protect dynamic user state Chang S. Bae
2021-08-18 16:24 ` Borislav Petkov
2021-08-18 17:20 ` Thiago Macieira
2021-08-18 17:46 ` Borislav Petkov
2021-08-18 17:58 ` Thiago Macieira
2021-08-18 18:10 ` Borislav Petkov
2021-08-24 22:51 ` Len Brown
2021-08-18 20:43 ` Bae, Chang Seok
2021-08-18 21:04 ` Thiago Macieira
2021-08-18 21:12 ` Bae, Chang Seok
2021-08-18 22:27 ` Thiago Macieira
2021-08-19 1:21 ` Andy Lutomirski
2021-08-19 16:06 ` Thiago Macieira
2021-08-18 21:17 ` Borislav Petkov
2021-08-18 21:37 ` Bae, Chang Seok
2021-08-19 8:00 ` Borislav Petkov
2021-08-19 15:24 ` Bae, Chang Seok
2021-08-24 23:22 ` Len Brown
2021-08-30 17:31 ` Borislav Petkov
2021-09-17 3:48 ` Len Brown
2021-08-18 19:47 ` Bae, Chang Seok
2021-08-24 22:21 ` Len Brown
2021-08-30 17:41 ` Borislav Petkov
2021-08-31 21:44 ` Len Brown
2021-08-24 23:17 ` Len Brown
2021-08-30 17:53 ` Borislav Petkov
2021-08-31 22:07 ` Len Brown
2021-08-31 22:11 ` Dave Hansen
2021-08-30 18:04 ` Dave Hansen
2021-08-31 22:15 ` Len Brown
2021-08-31 22:16 ` Len Brown
2021-08-31 22:39 ` Thiago Macieira
2021-08-31 22:44 ` Len Brown
2021-07-30 14:59 ` [PATCH v9 13/26] x86/fpu/xstate: Support ptracer-induced XSTATE buffer expansion Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 14/26] x86/arch_prctl: Create ARCH_SET_STATE_ENABLE/ARCH_GET_STATE_ENABLE Chang S. Bae
2021-08-06 16:46 ` Thiago Macieira
2021-08-09 22:08 ` Bae, Chang Seok
2021-08-09 23:42 ` Thiago Macieira
2021-08-10 0:57 ` Bae, Chang Seok
2021-08-13 19:44 ` Bae, Chang Seok
2021-07-30 14:59 ` [PATCH v9 15/26] x86/fpu/xstate: Support both legacy and expanded signal XSTATE size Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 16/26] x86/fpu/xstate: Adjust the XSAVE feature table to address gaps in state component numbers Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 17/26] x86/fpu/xstate: Disable XSTATE support if an inconsistent state is detected Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 18/26] x86/cpufeatures/amx: Enumerate Advanced Matrix Extension (AMX) feature bits Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 19/26] x86/fpu/amx: Define AMX state components and have it used for boot-time checks Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 20/26] x86/fpu/amx: Initialize child's AMX state Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 21/26] x86/fpu/amx: Enable the AMX feature in 64-bit mode Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 22/26] x86/fpu/xstate: Skip writing zeros to signal frame for dynamic user states if in INIT-state Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 23/26] selftest/x86/amx: Test cases for the AMX state management Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 24/26] x86/insn/amx: Add TILERELEASE instruction to the opcode map Chang S. Bae
2021-07-30 14:59 ` [PATCH v9 25/26] intel_idle/amx: Add SPR support with XTILEDATA capability Chang S. Bae
2021-07-30 18:41 ` Dave Hansen
2021-08-03 21:32 ` Bae, Chang Seok
2021-08-03 21:38 ` Dave Hansen
2021-08-03 21:43 ` Brown, Len
2021-07-30 20:15 ` Dave Hansen
2021-07-30 14:59 ` [PATCH v9 26/26] x86/fpu/xstate: Add a sanity check for XFD state when saving XSTATE 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=2BF12EDA-89F0-40F7-B63E-50ADD0262164@intel.com \
--to=chang.seok.bae@intel.com \
--cc=bp@alien8.de \
--cc=dave.hansen@intel.com \
--cc=jing2.liu@intel.com \
--cc=len.brown@intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mingo@kernel.org \
--cc=ravi.v.shankar@intel.com \
--cc=tglx@linutronix.de \
--cc=thiago.macieira@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).