From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Tony Luck <tony.luck@intel.com>,
Andy Lutomirski <luto@kernel.org>,
Rik van Riel <riel@surriel.com>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Fenghua Yu <fenghua.yu@intel.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2 8/8] x86/fpu/xstate: Restore supervisor xstates for __fpu__restore_sig()
Date: Tue, 10 Mar 2020 13:36:19 -0700 [thread overview]
Message-ID: <e62e968c0980b091d7b263401ddd10162773678f.camel@intel.com> (raw)
In-Reply-To: <20200306205039.GA5337@cz.tnic>
On Fri, 2020-03-06 at 21:50 +0100, Borislav Petkov wrote:
> On Wed, Mar 04, 2020 at 10:18:46AM -0800, Yu-cheng Yu wrote:
> > There is another way to keep this patch...
> >
> > if (xfeatures_mask_supervisor()) {
> > fpu->state.xsave.xfeatures &= xfeatures_mask_supervisor();
>
> Is the subsequent XSAVE in copy_user_to_fpregs_zeroing() going to
> restore the user bits in XSTATE_BV you just cleared?
>
> Sorry, it looks like it would but the SDM text is abysmal.
I checked and this won't work.
Earlier you wrote:
53973 / (3*60 + 35) =~ 251 XSAVES invocations per second!
I would argue that the kernel does much more than that for context
switches.
These are from:
perf record -a make -j32 bzImage
# Samples: 11M of event 'cycles'
# Event count (approx.): 7610600069602
#
# Overhead Symbol
2.19% [.] ht_lookup_with_hash
1.74% [.] _int_malloc
1.46% [.] _cpp_lex_token
1.46% [.] ggc_internal_alloc
1.10% [.] cpp_get_token_with_location
1.10% [.] malloc
1.05% [.] _int_free
0.71% [.] elf_read
0.70% [.] ggc_internal_cleared_alloc
0.69% [.] htab_find_slot
0.69% [.] c_lex_with_flags
0.61% [.] get_combined_adhoc_loc
0.57% [.] linemap_position_for_column
[...]
0.00% [.] 0x0000000000bad020
0.00% [.] 0x0000000000b4952b
0.00% [k] __fpu__restore_sig
Here, __fpu__restore_sig() actually takes very little percentage.
Consider this and later maintenance, I think copy_xregs_to_kernel() is at
least not worse than saving each state separately.
Yu-cheng
next prev parent reply other threads:[~2020-03-10 20:36 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-21 20:18 [PATCH v2 0/8] Support XSAVES supervisor states Yu-cheng Yu
2020-01-21 20:18 ` [PATCH v2 1/8] x86/fpu/xstate: Define new macros for supervisor and user xstates Yu-cheng Yu
2020-02-20 11:47 ` Borislav Petkov
2020-02-20 20:23 ` Yu-cheng Yu
2020-01-21 20:18 ` [PATCH v2 2/8] x86/fpu/xstate: Separate user and supervisor xfeatures mask Yu-cheng Yu
2020-02-21 10:34 ` Borislav Petkov
2020-01-21 20:18 ` [PATCH v2 3/8] x86/fpu/xstate: Introduce XSAVES supervisor states Yu-cheng Yu
2020-01-21 20:18 ` [PATCH v2 4/8] x86/fpu/xstate: Define new functions for clearing fpregs and xstates Yu-cheng Yu
2020-02-21 14:04 ` Borislav Petkov
2020-01-21 20:18 ` [PATCH v2 5/8] x86/fpu/xstate: Rename validate_xstate_header() to validate_xstate_header_from_user() Yu-cheng Yu
2020-02-21 14:13 ` Borislav Petkov
2020-01-21 20:18 ` [PATCH v2 6/8] x86/fpu/xstate: Update sanitize_restored_xstate() for supervisor xstates Yu-cheng Yu
2020-02-21 14:30 ` Borislav Petkov
2020-01-21 20:18 ` [PATCH v2 7/8] x86/fpu/xstate: Update copy_kernel_to_xregs_err() for XSAVES supervisor states Yu-cheng Yu
2020-01-21 20:18 ` [PATCH v2 8/8] x86/fpu/xstate: Restore supervisor xstates for __fpu__restore_sig() Yu-cheng Yu
2020-02-21 17:58 ` Borislav Petkov
2020-02-27 22:52 ` Yu-cheng Yu
2020-02-28 12:17 ` Borislav Petkov
2020-02-28 12:51 ` Sebastian Andrzej Siewior
2020-02-28 15:53 ` Yu-cheng Yu
2020-02-28 16:23 ` Borislav Petkov
2020-02-28 16:20 ` Yu-cheng Yu
2020-02-28 16:50 ` Sebastian Andrzej Siewior
2020-02-28 16:54 ` Yu-cheng Yu
2020-02-28 17:22 ` Borislav Petkov
2020-02-28 18:11 ` Yu-cheng Yu
2020-02-28 18:31 ` Borislav Petkov
2020-02-28 21:22 ` Yu-cheng Yu
2020-02-28 21:47 ` Borislav Petkov
2020-02-28 22:13 ` Yu-cheng Yu
2020-02-29 14:36 ` Borislav Petkov
2020-03-02 18:09 ` Yu-cheng Yu
2020-03-04 18:18 ` Yu-cheng Yu
2020-03-06 20:50 ` Borislav Petkov
2020-03-10 20:36 ` Yu-cheng Yu [this message]
2020-03-10 21:16 ` Thomas Gleixner
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