From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Borislav Petkov <bp@alien8.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
"Andy Lutomirski" <luto@kernel.org>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
kvm@vger.kernel.org, "Jason A. Donenfeld" <Jason@zx2c4.com>,
"Rik van Riel" <riel@surriel.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>
Subject: Re: [PATCH 11/29] x86/fpu: Always init the `state' in fpu__clear()
Date: Thu, 13 Dec 2018 15:35:53 +0100 [thread overview]
Message-ID: <20181213143553.7ktfajxeewgiclxa@linutronix.de> (raw)
In-Reply-To: <20181212171129.GD6653@zn.tnic>
On 2018-12-12 18:11:29 [+0100], Borislav Petkov wrote:
> > diff --git a/arch/x86/math-emu/fpu_entry.c b/arch/x86/math-emu/fpu_entry.c
> > index 9e2ba7e667f61..a873da6b46d6b 100644
> > --- a/arch/x86/math-emu/fpu_entry.c
> > +++ b/arch/x86/math-emu/fpu_entry.c
> > @@ -113,9 +113,6 @@ void math_emulate(struct math_emu_info *info)
> > unsigned long code_base = 0;
> > unsigned long code_limit = 0; /* Initialized to stop compiler warnings */
> > struct desc_struct code_descriptor;
> > - struct fpu *fpu = ¤t->thread.fpu;
> > -
> > - fpu__initialize(fpu);
>
> Ok, you're removing it here but where is the FPU going to be initialized
> now in the FPU-less case?
>
> IOW, it is not clear to me where fpu__clear() get called for the FPU
> emulation case now...
During fork() fpu__initialize() is called for both (with and without
FPU) systems. The difference is made in fpu__clear() where the init is
avoided in the FPU-less case. With this hunk:
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -365,8 +364,8 @@ void fpu__clear(struct fpu *fpu)
/*
* Make sure fpstate is cleared and initialized.
*/
+ fpu__initialize(fpu);
if (static_cpu_has(X86_FEATURE_FPU)) {
- fpu__initialize(fpu);
user_fpu_begin();
copy_init_fpstate_to_fpregs();
}
we have the initialization in both cases.
The only "negative" thing might be that we now have a memset(, 0, 684)
(fpstate_init_soft()) during fork which would be avoided in case the
FPU-less system has a userland which is compiled with a soft-FPU toolchain.
I would worry about it once someone complains (and I doubt someone
complains even if we remove soft FPU support).
Sebastian
next prev parent reply other threads:[~2018-12-13 14:35 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-28 22:20 [PATCH v5] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 01/29] x86/fpu: Use ULL for shift in xfeature_uncompacted_offset() Sebastian Andrzej Siewior
2018-11-29 1:52 ` Rik van Riel
2018-12-03 21:00 ` [tip:x86/fpu] x86/fpu: Use unsigned long long " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 02/29] x86/entry/32: Remove asm/math_emu.h include Sebastian Andrzej Siewior
2018-11-29 1:52 ` Rik van Riel
2018-12-03 21:01 ` [tip:x86/fpu] x86/process/32: " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 03/29] x86/entry: Remove _TIF_ALLWORK_MASK Sebastian Andrzej Siewior
2018-11-29 1:53 ` Rik van Riel
2018-12-03 21:02 ` [tip:x86/fpu] x86/thread_info: " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 04/29] x86/pkeys: Make init_pkru_value static Sebastian Andrzej Siewior
2018-11-29 1:53 ` Rik van Riel
2018-12-03 21:02 ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 05/29] x86/fpu: add might_fault() to user_insn() Sebastian Andrzej Siewior
2018-11-29 1:54 ` Rik van Riel
2018-12-03 21:03 ` [tip:x86/fpu] x86/fpu: Add " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 06/29] x86/fpu: Update comment for __raw_xsave_addr() Sebastian Andrzej Siewior
2018-11-29 1:56 ` Rik van Riel
2018-12-03 21:03 ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 07/29] x86/fpu: don't export __kernel_fpu_{begin|end}() Sebastian Andrzej Siewior
2018-11-29 2:00 ` Rik van Riel
2018-11-29 15:02 ` [PATCH 07/29 v2] " Sebastian Andrzej Siewior
2018-12-03 21:04 ` [tip:x86/fpu] x86/fpu: Don't export __kernel_fpu_{begin,end}() tip-bot for Sebastian Andrzej Siewior
2018-12-03 21:12 ` Ard Biesheuvel
2018-12-03 22:08 ` Borislav Petkov
2018-12-04 11:39 ` Borislav Petkov
2018-12-04 12:15 ` Sebastian Andrzej Siewior
2018-12-04 12:33 ` Borislav Petkov
2018-12-04 11:45 ` tip-bot for Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 08/29] x86/fpu: Remove fpu->initialized usage in __fpu__restore_sig() Sebastian Andrzej Siewior
2018-12-06 20:07 ` Borislav Petkov
2018-12-07 8:17 ` Sebastian Andrzej Siewior
2018-12-07 10:19 ` Borislav Petkov
2018-11-28 22:20 ` [PATCH 09/29] x86/fpu: Remove fpu__restore() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 10/29] x86/fpu: Remove preempt_disable() in fpu__clear() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 11/29] x86/fpu: Always init the `state' " Sebastian Andrzej Siewior
2018-12-12 17:11 ` Borislav Petkov
2018-12-13 14:35 ` Sebastian Andrzej Siewior [this message]
2018-11-28 22:20 ` [PATCH 12/29] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 13/29] x86/fpu: Don't save fxregs for ia32 frames " Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 14/29] x86/fpu: Remove fpu->initialized Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 15/29] x86/fpu: Remove user_fpu_begin() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 16/29] x86/fpu: Add (__)make_fpregs_active helpers Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 17/29] x86/fpu: Make __raw_xsave_addr() use feature number instead of mask Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 18/29] x86/fpu: Make get_xsave_field_ptr() and get_xsave_addr() " Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 19/29] x86/fpu: Only write PKRU if it is different from current Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 20/29] x86/pkeys: Don't check if PKRU is zero before writting it Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 21/29] x86/fpu: Eager switch PKRU state Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 22/29] x86/entry: Add TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 23/29] x86/fpu: Always store the registers in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 24/29] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 25/29] x86/fpu: Update xstate's PKRU value on write_pkru() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 26/29] x86/fpu: Inline copy_user_to_fpregs_zeroing() Sebastian Andrzej Siewior
2018-11-28 23:09 ` Joey Pabalinas
2018-11-28 22:20 ` [PATCH 27/29] x86/fpu: Let __fpu__restore_sig() restore the !32bit+fxsr frame from kernel memory Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 28/29] x86/fpu: Merge the two code paths in __fpu__restore_sig() Sebastian Andrzej Siewior
2018-11-28 22:20 ` [PATCH 29/29] x86/fpu: Defer FPU state load until return to userspace Sebastian Andrzej Siewior
2018-11-29 15:00 ` Sebastian Andrzej Siewior
2018-12-10 14:41 ` Sebastian Andrzej Siewior
2018-11-30 11:52 ` [PATCH v5] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
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